- 


\\- 


ON  BALANTIDIUM  COLI  (MALMSTEN)  AND 

BALANTIDIUM  SUIS  (SP.  NOV.),  WITH 

AN  ACCOUNT  OF  THEIR  NEURO- 

MOTOR  APPARATUS 


A  THESIS  ACCEPTED  IN  PARTIAL  SATISFACTION  OF 
THE  REQUIREMENTS  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 
AT  THE  UNIVERSITY  OF  CALIFORNIA 


BY 


JAMES  DALEY  McDONALD 


1922 


'    • '  •  •      «•    *•- 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

IN 

ZOOLOGY 

Vol.  20,  No.  10,  pp.  243-300,  pis.  27-28,  15  figures  in  text  May  8,  1922 


ON   BALANTIDIUM  COLI   (MALMSTEN)   AND 

BALANTIDIUM  SUIS  (SP.  NOV.),  WITH 

AN  ACCOUNT  OF  THEIR  NEURO- 

MOTOR  APPARATUS 


BY 

j.  DALEY  MCDONALD 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY,  CALIFORNIA 

1922 


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1917  35 

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Bay,  California,  by  Albert  L.  Barrows.    Pp.  27-43.    December,  1917  .20 

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fornia, by  Christine  Essenberg.    Pp.  45-60,  plates  2-3.    October,  1917 20 

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berg.    Pp.  61-74,  plates  4-5.    October,  1917  15 

5.  Crithidia  euryophthalmi,  sp.  nov.,  from  the  Hemipteran  Bug,  Eury aphtha! mus 

convivus  Stal,  by  Irene  McCulloch.    Pp.  75-88,  35  figures  in  text.    Decem- 
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Earthworm,  by  John  F.  Bovard.    Pp.  103-134,  14  figures  in  text.    January, 

1918 35 

8.  The  Function  of  the  Giant  Fibers  in  Earthworms,  by  John  F.  Bovard.    Pp. 

135-144,  1  figure  in  text.    January,  1918 10 

9.  A  Rapid  Method  for  the  Detection  of  Protozoan  Cysts  in  Mammalian 

Faeces,  by  William  C.  Boeck.    Pp.  145-149.    December,  1917 05 

10.  The  Musculature  of  Heptanchus  maculatus,  by  Pirie  Davidson.    Pp.  151-170, 

12  figures  in  text.    March,  1918 25 

11.  The  Factors  Controlling  the  Distribution  of  the  Polynoidae  of  the  Pacific 

Coast  of  North  America,  by  Christine  Essenberg.    Pp.  171-238,  plates  6-8, 

2  figures  in  text.    March,  1918 75 

12.  Differentials  in  Behavior  of  the  Two  Generations  of  Salpa  democratica 

Relative  to  the  Temperature  of  the  Sea,  by  Ellis  L.  Michael.    Pp.  239-298, 
plates  9-11,  1  figure  in  text.    March,  1918  65 

13.  A  Quantitative  Analysis  of  the  Molluscan  Fauna  of  San  Francisco  Bay,  by 

E.  L.  Packard.    Pp.  299-336,  plates  12-13,  6  figures  in  text.    April,  1918 40 

14.  The  Neuromotor  Apparatus  of  Euplotcs  patella,  by  Harry  B.  Yocom.    Pp. 

337-396,  plates  14-16.    September,  1918  70 

15.  The  Significance  of  Skeletal  Variations  in  the  Genus  Peridinium,  by  A.  L. 

Barrows.    Pp.  397-478,  plates  17-20,  19  figures  in  text.    June,  1918 90 


' 

* ' J  J 


ON  BALANTIDIUM  COL I  (Malmsten)  AND  BALANTIDIUM  St 
WITH  AN  ACCOUNT  OF  THE i NEUROMOTOR  APPARj 


by 

J.Daley  McDonald 


-  0  - 


Submitted  in  partial  fulfillment  of  the  requir* 
for  the  degree  of  Doctor  of  Philosophy 


Is  Approved  :     ci-fr^  Pasadena,  California 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

IN 

ZOOLOGY 

Vol.  20,  No.  10,  pp.  243-300,  pis.  27-28,  15  figures  in  text  May  8,  1922 


ON  BALANTIDIUM  COLI   (MALMSTEN)   AND 

BALANTIDIUM  SUIS  (SP.  NOV.),  WITH 

AN  ACCOUNT  OF  THEIR  NEURO- 

MOTOR  APPARATUS 

BY 

j.  DALEY  MCDONALD 


CONTENTS  PAGE 

Introduction 244 

Acknowledgments : 245 

Material  and  technique 245 

Occurrence  and  geographic  distribution 246 

Studies  of  living  organisms 246 

Systematic  position  of  genus  and  species 248 

Balantidium  coli 249 

Balantidium  suis  sp.  nov 250 

Method  and  use  of  measurements 254 

Other  specific  characters 258 

Balantidium  from  man 261 

Morphology 262 

Ectoplasmic  structures 263 

Pellicle , 263 

Ectoplasm 266 

Cilia 270 

Basal  apparatus  of  cilia 271 

Ciliary  movements 273 

Cytostome 276 

Oral  plug 280 

Contractile  vacuoles 280 

Endoplasmic  structures 282 

Endoplasm 282 

Food  vacuoles , '. 282 

Macronucleus 282 

Micronucleus 283 

Neuromotor  apparatus 284 

Motorium .' 285 

Circumoesophageal  fiber 285 

Adoral  ciliary  fiber 286 


244  University  of  California  Publications  in  Zoology       [VOL.  20 

PAGE 

Adoral  ciliary  rootlets 286 

Radial  fibers . 286 

Discussion 288 

Summary 293 

Literature  cited , 294 

Explanation  of  plates 298 


INTRODUCTION 

The  earliest  observation  of  Protozoa  of  the  genus  Balantidium  has 
in  several  instances  been  accredited  to  Antony  von  Leeuwenhoek 
(1708).  During  an  attack  of  dysentery  he  detected  motile  organisms 
in  the  discharges.  At  that  time  no  discrimination  had  been  made 
between  ciliated  and  flagellated  protozoa  and  his  account  of  his  obser- 
vations is  not  sufficiently  complete  to  make  possible  the  classification 
of  the  organisms  which  he  found.  However,  he  stated  that  they  were 
about  the  size  of  red  blood  corpuscles,  which  would  indicate  that  they 
were  intestinal  flagellates  and  not  Balantidium,  which  is  very  much 
larger. 

Malmsten  (1857)  was  the  first  to  describe  Balantidium  coli.  This 
species  has  become  better  known  than  the  other  species  of  the  genus, 
due  to  its  being  the  cause  of  a  specific  dysentery  known  as  balantidiasis. 
Two  persons  suffering  from  this  disease  came  to  Malmsten  for  medical 
attention  during  1856-57.  Pie  was  assisted  in  the  study  of  protozoans 
which  he  found  in  the  excreta  from  these  two  patients  by  the  zoologist 
Loven  who  believed  that  the  parasites  were  new  to  science  and  so  pre- 
pared a  careful  description  of  them  accompanied  by  figures.  For  the 
organism  they  suggested  the  name  Paramoecium  ( ?)  coli.  Since  that 
time  infections  with  Balantiddum  coli  have  been  reported  in  increasing 
numbers  and  some  cytological  studies 'have  been  made,  though  much 
more  attention  has  been  given  to  the  problems  of  prophylaxis  and 
treatment  of  the  disease  which  this  species  causes  than  to  the  parasite 
itself. 

The  first  record  of  Balantidium  coli  as  a  parasite  of  pigs  was  made 
by  Leuckart  (1861).  Stein  (1862)  also  studied  these  forms  from  pigs 
and  he  was  the  first  to  assign  them  to  the  genus  Balantidium.  The 
genus  had  been  established  by  Claparede  and  Lachmann  (1858)  with 
Balantidium  entozoon  from  the  frog  as  the  type  species.  More  recently 
Strong  (1904),  Brumpt  (1909),  Walker  (1913),  and  others  have  car- 
ried on  investigations  on  this  parasite  of  pigs  in  order  to  become 
acquainted  with  the  problems  involved  in  the  infection  of  man. 


1922]      McDonald:  On  Balantidium  eoli  and  Balantidium  suis      245 


ACKNOWLEDGMENTS 

It  has  been  my  privilege  to  study  the  morphology  of  Batantidium 
coli  and  Balantidium  suis  (sp.  nov.)  under  the  direction  of  Professor 
Charles  A.  Kof  oid,  to  whom  I  am  indebted  for  helpful  suggestions  and 
for  oversight  of  the  entire  work.  Acknowledgment  is  due  Professor 
William  W.  Cort  for  many  valuable  criticisms.  I  also  take  this  oppor- 
tunity to  express  my  appreciation  of  the  courtesy  of  Mr.  E.  B.  Brown, 
superintendent  of  the  Oakland  Meat  and  Packing  Company,  who 
kindly  granted  me  permission  to  work  in  the  company's  abattoir  and 
also  facilitated  the  work  in  every  possible  way. 


MATERIAL  AND  TECHNIQUE 

The  material  for  these  studies  was  obtained  almost  exclusively  from 
pigs  killed  by  the  Oakland  Meat  and  Packing  Company,  Stockyards, 
California.  At  their  abattoir  I  was  permitted  to  work  in  the  room 
where  the  pigs  were  dressed,  which  made  it  possible  to  obtain  the 
material  from  the  intestine  before  it  had  cooled  below  the  normal  body 
temperature.  To  determine  the  presence  of  the  balantidia  a  small  slit 
was  made  in  the  caecum  and  a  drop  of  the  contents  withdrawn  with 
a  pipette.  This  drop  was  quickly  placed  on  a  warm  slide  and  exam- 
ined with  a  microscope.  If  the  animals  were  present  they  would  be 
detected  very  readily  for  they  are  exceedingly  active ;  in  most  cases 
they  occurred  in  numbers  sufficiently  large  that  from  one  to  ten  could 
be  seen  in  every  field  when  a  16  mm.  objective  was  used.  This  method 
was  rapid  enough  to  allow  all  pigs  to  be  examined  as  fast  as  they  were 
killed  and  dressed. 

A  sample  from  the  caecum  was  not  relied  upon  as  critical  in  the 
determination  of  infection  until  examination  of  the  entire  length  of 
the  intestine  had  been  made  in  several  instances.  In  order  to  discover 
the  normal  distribution  throughout  the  intestine  it  was  removed  entire 
and  taken  to  the  laboratory  of  the  abattoir.  Incisions  were  made  every 
one  or  two  feet,  beginning  with  the  duodenum  and  continuing  to  the 
rectum,  and  samples  examined  from  each  of  these  incisions.  In  no 
cases  were  balantidia  found  more  than  three  feet  above  the  ileocaecal 
valve,  and  only  in  two  or  three  instances  were  any  at  all  present  in 


246  University  of  California  Publications  in  Zoology       [VoL- 20 

the  small  intestine.  In  the  caecum  and  first  three  or  four  feet  of  the 
colon  the  balantidia  were  always  more  active  and  more  numerous  than 
elsewhere.  Posteriorly  from  this  region  they  were  found  in  progressive 
stages  of  encystment  until  in  the  rectum  the  majority  were  completely 
encysted. 

OCCURRENCE  AND  GEOGRAPHIC  DISTRIBUTION 

Approximately  200  pigs  were  examined.  They  had  been  raised  in 
the  Sacramento  Valley,  except  for  one  lot  from  Los  Banos,  California, 
and  a  lot  from  the  state  of  Nevada.  Of  the  200  pigs  examined  68 
per  cent  were  infected.  The  examinations  were  made  at  nine  separate 
times  between  September,  1913,  and  May,  1918,  ten  to  sixty  individuals 
being  examined  each  time.  In  five  of  the  nine  lots  every  pig  was 
found  to  be  infected.  The  lowest  percentage  of  infection  was  13  per 
cent,  in  the  lot  shipped  from  Nevada.  This  indicates  a  very  general 
infection  of  pigs  with  Balantidium  in  this  region  of  the  United  States. 

Stiles  (cit.  Strong,  1904),  Bel  and  Couret  (1910),  and  others  have 
previously  found  the  organisms  in  pigs  in  the  United  States.  Leuckart 
(1861),  working  in  Germany,  was  the  first  to  find  Balantidium  in  pigs. 
Since  then  Stein  (1862),  Eckecrantz  (1869),  and  Prowazek  (1913) 
have  reported  them  from  the  same  country.  In  1871  Wising  noted 
their  occurrence  in  pigs  in  Sweden.  Grassi  (1882)  and  Calandruccio 
(1888)  have  found  the  parasites  in  swine  in  Italy.  Rapchevski  (1882) 
reported  the  occurrence  of  balantidia  in  Russia.  In  France  they  have 
been  found  in  pigs  by  Railliet  (1886),  Neumann  (1888),  and  Brumpt 
(1909).  Strong  (1904),  Walker  (1913),  and  several  others  have 
noted  the  occurrence  in  pigs  in  the  Philippine  Islands.  Similar  reports 
from  China  have  been  made  by  Maxwell  (1912),  and  Mason  (1919)  ; 
from  Cuba  by  Taboadela  (1911)  ;  and  from  South  America  by  Bayana 
(1918).  These  citations  indicate  that  BalantiMum  coli  is  probably  as 
widely  distributed  geographically  as  is  its  host,  the  pig. 


STUDIES  OF  LIVING  ORGANISMS 

The  balantidia  are  very  sensitive  to  changes  of  temperature.  When 
the  medium  in  which  they  are  swimming  is  cooled  a  few  degrees  they 
slow  up  their  movements  very  decidedly.  After  a  time  they  become 
almost  perfectly  spherical,  in  which  form  their  activitiy  is  restricted 
to  a  rotary  motion  with  little  or  no  progression.  In  this  condition  they 
will  live  for  six  or  eight  hours  at  ordinary  room  temperature. 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      247 

In  order  to  avoid  the  deleterious  effects  caused  by  cooling  and  by 
increased  bacterial  action,  most  of  the  studies  on  living  organisms  were 
made  at  the  abattoir.  When  continuous  observation  over  a  long  period 
was  desired,  however,  the  material  was  conveyed  to  the  laboratory  in 
thermos  bottles  and  kept  in  the  incubator  at  37.5°  C.  In  tfris~manner 
material  could  be  kept  for  three  days.  Ultimate  degeneration  of  the 
organisms  seemed  to  be  due  more  to  the  increase  in  the  bacterial  con- 
tent of  the  medium  than  to  any  other  cause.  During  observation  either 
an  electric  warm  stage  or  the  microscope  warm  oven  designed  by  Long 
(1912)  was  employed.  Of  the  several  vital  stains  used,  neutral 
red  proved  most  satisfactory  in  the  differentiation  of  the  neuromotor 
apparatus. 

Fixation  and  staining. — The  following  fixatives  were  used :  Schau- 
dinn's  fluid,  Zenker's  fluid,  formalin,  osmic  acid,  and  picromercuric 
fluid  (according  to  the  formula  by  A.  D.  Drew,  used  by  Yocom,  1912). 
Quick  action  was  one  of  the  most  important  factors  in  the  fixation, 
and  was  usually  obtained  by  having  the  killing  fluid  hot  (60-80°  C.) 
and  using  an  amount  at  least  equal  to  the  amount  of  the  material  to 
be  fixed.  Frequently  the  action  was  so  nearly  instantaneous  that  the 
cilia  on  the  killed  animals  retained  their  exact  relative  position  (see 
fig.  N).  After  fixation  the  material  was  thoroughly  washed,  iodine 
alcohol  being  used  if  mercurial  salts  were  present.  Material  was  pre- 
served in  70  per  cent  alcohol. 

Before  staining,  the  preserved  material  was  usually  concen- 
trated by  elimination  of  lighter  debris  by  centrifuging  and  the  heavier 
by  sedimentation.  Water  was  found  to  be  a  more  satisfactory  medium 
for  these  operations  than  either  alcohol  or  salt  solutions.  In  case  sec- 
tions were  to  be  made,  additional  care  was  taken  in  the  concentration 
process  and  then  the  material  was  handled  according  to  the  methods 
employed  by  Metcalf  (1909)  and  by  Sharp  (1914). 

Iron  haematoxylin  gave  uniformly  the  best  results  in  staining.  For 
cysts,  however,  on  account  of  their  imperviousness,  it  was  necessary  to 
use  Delafield's  haematoxylin  to  which  had  been  added  a  small  amount 
of  acetic  acid.  In  addition  to  the  first  mentioned  stain,  Mallory's  con- 
nective tissue  stain  was  used  on  sections. 


248 


University  of  California  Publications  in  Zoology       [V°L-  20 


SYSTEMATIC  POSITION  OF  GENUS  AND  SPECIES 

Claparede  and  Lachmann  (1858)  removed  Bursaria  entozoon  from 
the  genus  in  which  it  had  been  placed  by  Ehrenberg  (1838)  and 
created  for  it  the  new  genus  Balantidium.  This  genus  was  of  the 
family  Bursaridae  and  the  order  Heterotricha.  The  twenty-two  species 
of  the  genus  that  have  been  described  to  date  are  listed  below. 


KNOWN  SPEOIES  OF  THE  GENUS  BALANTIDIUM 


Species 
Balantidium  entozoon 

Balantidium  coli 

Balantidium  duodeni 
Balantidium  elongatum 


Balantidium  medusarum 
Balantidium  amphictenides 

Balantidium  gyrans 
Balantidium  viride 
Balantidium  minutum 
Balantidium  giganteum 
Balantidium  helenae 


Balantidium  graeile 


Balantidium 
Balantidium 
Balantidium 
Balantidium 
Balantidium 
Balantidium 
Balantidium 
Balantidium 
Balantidium 
Balantidium 


rotundum 

faleiformis 

ovale 

hyalinum 

littorinae 

testudinis 

hydrae 

piscicola 

caviae 

orchestia 


Original  description  by 
Ehrenberg,  1838 

Malmsten,  1857 

Stein,  1862 
Stein,  1862 


Mereschkowsky,  1879 
Entz,  Sr.,  1888 

Kellicott,  1889 
Willach,  1893 
Schaudinn,  1899 
Bezzenberger,  1903 
Bezzenberger,  1903 


Bezzenberger,  1903 

Bezzenberger,  1903 
Walker,  1909 
Dobell,  1910 
Dobell,  1910 
Chagas,  1911 
Chagas,  1911 
Entz,  Jr.,  1913 
Entz,  Jr.,  1913 
Neiva  et  al,  1914 
Watson,  1916 


Hosts 

Rana  esculenta 
Rana  temporaria 
Sus  scrofa 
Homo  sapiens 
Ban  a  esculenta 
Triton  cristatus 
Triton  alpestris 
Triton  marmoratus 
Rana  esculenta 
Rana  temporaria 
Bougainvillea,  Obelia, 
Eucope,  Broda  sp.? 
Amphictenis, 
Turbellaria  marina 
Aquatic  worm 
Columba  sp.? 
Homo  sapiens 
Rana  esculenta 
Rana  cyanophlyctis 
Rana  tigrina 
Rana  limnocharis 
Rana  hexadactyla 
Rana  cyanophlyctis 
Rana  hexadactyla 
Rana  esculenta 
Rana  palustris 
Rana  tigrina 
Rana  tigrina 
Littorina 
Testudo  graeca 
Hydra  olygactis 
Piarectus  brachypomus 
Cavia  aperea 
Orchestia  agilis 
Talorchestia  longicornis 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      249 

The  wide  diversity  of  hosts,  ranging  from  hydroids  and  crustaceans 
to  the  warm-blooded  vertebrates,  including  man,  must  demand  a  wide 
versatility  on  the  part  of  the  parasite.  Considerable  structural  varia- 
tion is  apparent  even  on  cursory  examination,  and  some  of  these 
structural  differences  might  be  sufficiently  marked  to  servTT  for  generic 
differentiation.  A  new  generic  division  would  seem  desirable,  but  the 
suggestions  of  Biitschli  (1884)  and  Schweier  (1900)  in  this  direction 
have  not  been  generally  accepted. 

BALANTIDIUM  COLI  MALMSTEN   (1857) 

SYNONOMY: 

Paramoecium  (?}  coli  Malmsten,  1857. 
Plagiotoma  coli,  Claparede  and  Lachmann,  1858. 
Leucophyra  coli,  Stein,  1860. 
Holophyra  coli,  Leuckart,  1861. 
Balantidium  coli,  Stein,  1862. 

Up  to  the  present  time  only  one  species,  Balantidium  coli,  has  been 
described  as  parasitic  in  pigs.  It  was  first  described  by  Malmsten 
(1857)  who,  noting  its  likeness  to  Paramoecium  colpoda  (Ehrenberg), 
suggested  the  name  Paramoecium  (?)  coli.  During  the  following  year, 
Claparede  and  Lachmann  (1858)  reproduced  one  of  Malmsten 's  orig- 
inal figures  and  after  considering  his  description  transferred  the 
species  to  the  genus  Plagiotoma.  In  1860,  Stein,  using  the  description 
by  Malmsten  (1857),  pointed  out  that  the  organism  was  not  a  Para- 
moecium and  Relieved  that  it  properly  belonged  in  the  genus  Leuco- 
phyra. Leuckart  in  1861  discovered  a  ciliate  in  the  intestine  of  pigs 
which  he  concluded  was  identical  with  the  one  already  described,  but 
he  was  not  satisfied  with  the  genus  to  which  it  had  been  assigned  by 
Stein  (1861)  and  believed  that  its  closest  relation  was  with  Holophyra 
in  which  genus  it  should  be  placed.  In.  1863  he  still  retained  this  view 
but  suggested  the  appropriateness  of  the  establishment  of  a  new  genus. 
But  Stein  (1862)  had  already  recognized  those  characters  of  the 
species  which  showed  its  close  relation  to  Balantidium  entozoon  and 
had  placed  it  in  the  genus  Balantidium. 

During  the  present  investigation  the  following  specific  character- 
istics have  been  found  very  constant.  The  individuals  of  the  species 
Balantidium  coli  are  ovoid  in  form,  the  more  pointed  end  being  an- 
terior; length  varies  from  30/*  to  150/t;  breadth  varies  from  25,/A  to 
120ju, ;  in  the  majority  of  individuals  the  length  is  1.3  times  the  breadth ; 
the  greatest  transverse  diameter  intersects  the  longitudinal  axis  poster- 


250  University  of  California  Publications  in  Zoology       [VoL- 20 

ior  to  its  midpoint;  the  adoral  zone  is  approximately  terminal,  and 
the  anterior  tip  of  the  body  lies  within  it;  the  plane  of  demarcation 
between  the  apical  cone  of  the  ectoplasm  and  the  endoplasm  is  approx- 
imately at  right  angles  to  the  long  axis  of  the  body ;  the  macronucleus 
is  elongate  but  the  length  usually  does  not  exceed  three  times  the 
breadth;  two  contractile  vacuoles  are  present,  a  smaller  one  located 
anteriorly  and  a  larger  one  located  posteriorly;  a  posterior  cytopyge 
is  usually  distinctly  visible. 

BALANTIDIUM  suis  SP.  NOV. 

Early  in  the  work  of  examining  pigs  for  Balantidium  coli  it  became 
evident  that  this  protozoan  showed  extreme  variation  in  shape.  In 
many  instances  the  diversity  occurred  among  individuals  from  the 
same  host.  Further  observations  led  me  to  believe  that  there  were 
two  fairly  distinct  types,  the  one,  longer  and  more  slender  as  compared 
with  the  other  which  was  distinctly  ovoid.  Measurements  have  been 
recorded  by  various  writers  of  Balantidium  coli  from  man.  Malmsten 
(1857)  in  the  original  description  gave  the  length  as  60-10CV;  breadth, 
50-70/i.  Solojew  (1901)  recorded  the  length  as  65/*,  the  breadth  as 
40/A.  Wising  (1871)  states  that  the  length  varies  from  50-100/z,  while 
the  breadth  varies  from  40-50/*.  Prowazek  (1913)  gave  the  length  as 
52-71/x,  the  breadth,  40-58/*.  Leuckart  (1861)  measured  balantidia 
from  swine  and  found  the  length  to  be  75-110/x  and  the  breadth  70/x. 
Still  others  give  dimensions,  but  all  are  inadequate  for  the  determina- 
tion of  the  occurrence  of  types  with  distinct  proportions.  First,  with 
one  or  two  exceptions  all  dimensions  have  been  taken  of  balantidia 
found  in  man,  and  from  these  it  might  not  be  safe  to  draw  conclusions 
regarding  diversity  among  those  found  in  pigs.  In  the  second  place, 
the  measurements  given  are  either  averages  or  else  represent  extreme 
limits.  In  either  case  they  are  practically  useless  in  determining  indi- 
vidual variations,  for  even  in  the  case  of  extreme  types  the  range 
between  limits  is  so  great  that  two,  or  even  more,  distinct  types,  based 
on  proportions  of  breadth  to  length,  might  be  included.  Nowhere 
has  there  been  found  a  series  of  individual  measurements  which  would 
make  it  possible  to  determine  whether  variations  were  continuous  or 
discontinuous.  To  obtain  such  a  series  of  measurements  was  the  pur- 
pose of  the  phase  of  the  work  about  to  be  described. 

Material  which  was  to  be  used  in  taking  the  measurements  was 
killed  and  preserved  with  all  possible  care.  Hot  Schaudinn's  fluid 
was  used  in  all  cases,  the  material  being  quickly  and  thoroughly  mixed 


1922]       McDonald:  On  Balantid/ium  coli  and  Balantidium  suis      251 

into  a  large  quantity  of  it  so  that  action  would  be  as  nearly  instan- 
taneous as  possible,  thus  avoiding  distortion.  Osmic  acid  vapor  was 
tried  but  Schaudinn's  fluid  gave  equally  good  results  and  was  more 
convenient  for  manipulation.  Material  was  never  allowed  to  cool 
before  fixing,  for  on  cooling  the  individuals  tend  to  become  spherical. 
Several  attempts  were  made  to  measure  living  organisms  but  their 
ceaseless  activity  at  normal  temperature  (.37.5°  C)  made  this  almost 
impossible  and  slowing  them  up  by  the  use  of  Irish  moss  or  by  cooling, 
as  mentioned  above,  caused  them  to  become  distorted.  If  there  were 
changes  due  to  fixation,  the  logical  expectation  would  be  that  the  error 
would  be  on  the  side  of  conservatism  for  such  changes  would  tend  to 
obliterate  rather  than  accentuate  the  division  into  two  groups ;  for  the 
shape  of  the  elongate  forms  would  be  more  changed  by  the  fixative, 
the  tendency  being  for  them  to  shorten  and  broaden  and  thus  approach 
the  ovoid  type.  However,  in  the  method  of  fixation  used,  I  am  sure 
that  distortion  was  so  slight  as  to  be  negligible. 

Following  fixation  the  material  was  carefully  washed  and  carried 
slowly  through  the  lower  grades  of  alcohol  to  70  per  cent  in  which 
the  material  was  kept  for  measuring.  A  drop  of  the  material  from 
which  measurements  were  to  be  taken  was  placed  on  a  slide,  covered 
with  a  coverglass,  the  excess  of  fluid  removed,  and  the  edges  sealed 
with  vaseline  to  prevent  evaporation.  Just  enough  fluid  was  removed 
from  under  the  coverglass  to  reduce  the  depth  of  the  medium  so  that 
the  majority  of  the  animals  would  lie  flat,  and  yet  not  enough  to  allow 
the  coverglass  to  exert  any  pressure.  The  exertion  of  pressure  on  the 
animals,  however,  would  ordinarily  be  prevented  by  the  presence  of 
large  particles  of  foreign  material.  •  The  object  of  having  animals  lie 
flat  on  the  slide  was  to  avoid  the  error  which  would  otherwise  be  caused 
by  foreshortening.  A  slight  elevation  of  one  end  would  make  con- 
siderable error  in  the  determination  of  the  length  of  the  animal. 

The  slide  was  then  placed  on  the  microscope  and  systematically 
examined  by  the  use  of  the  mechanical  stage.  Beginning  at  the  upper 
left-hand  corner  and  progressing  as  one  would  in  reading  a  book,  every 
individual  encountered  in  the  survey  was  measured.  The  only  excep- 
tions made  were  in  case  the  animal  was  not  lying  flat  or  showed  marked 
signs  of  distortion.  This  procedure  avoided  selection  which  might 
unconsciously  be  made  by  the  observer.  For  making  the  measurements 
a  4  mm.  objective  was  used  in  combination  with  an  ocular-micrometer 
inserted  in  9x  compensating  ocular.  With  the  magnification  given  by 
this  combination  the  limit  of  error  did  not  exceed  one  micron. 


252 


University  of  California  Publications  in  Zoology       [VOL.  20 


The  longitudinal  axis  and  the  longest  transverse  axis  of  each  indi- 
vidual were  measured,  and  the  ratio  of  length  to  breadth  computed 
(see  Table  I). 


TABLE  I 


COMPARATIVE  MEASUREMENTS  OF 
BALANTIDIUM  COLI 

INDIVIDUALS  FROM  PIG  No.  1 
(Bal.  suis,  with  five  exceptions) 


ONE  HUNDRED  INDIVIDUALS  EACH  OF 
AND  BALANTIDIUM  suis 

INDIVIDUALS  FROM  PIG  No.  4 
(Bal.  coli,  with  one  exception) 


Length  in 
microns 

Breadth  in 
microns 

Ratio  of 
length  to 
breadth 

Length  in 
microns 

Breadth  in 
microns 

Ratio  of 
length  to 
breadth 

114 

42 

2.71 

99 

75 

1.32 

108 

51 

2.11 

96 

81 

1.19 

63 

36 

1.75 

126 

75 

1.68* 

90 

45 

2.00 

118 

87 

1.36 

93 

48 

1.94 

111 

87 

1.28 

72 

39 

1.85 

87 

75 

1.16 

126 

69 

1.83 

90 

66 

1.36 

87 

48 

1.82 

105 

75 

1.40 

108 

57 

1.90 

78 

66 

1.18 

102 

54 

1.89 

90 

63 

1.43 

117 

51 

2.30 

87 

72 

1.21 

120 

57 

2.10 

87 

72 

1.21 

96 

42 

2.29 

99 

75 

1.32 

84 

39 

2.12 

105 

75 

1.40 

120 

48 

2.50 

89 

75 

1.19 

117 

48 

2.42 

81 

63 

1.28 

93 

51 

1.83 

81 

66 

1.23 

96 

51 

1.89 

75 

63 

1.19 

72 

57 

1.26* 

84 

69 

1.22 

75 

54 

1.39* 

69 

60 

1.15 

111 

51 

2.14 

90 

66 

1.36 

111 

54 

2.03 

93 

75 

1.23 

84 

36 

2.31 

87 

69 

1.26 

69 

39 

1.77 

90 

81 

1.11 

78 

51 

1.52* 

105 

90 

1.16 

81 

45 

1.80 

87 

69 

1.26 

111 

45 

2.42 

84 

72 

1.17 

81 

45 

1.80 

66 

58 

1.14 

84 

45 

1.86 

75 

60 

1.25 

90 

45 

2.00 

81 

63 

1.29 

84 

42 

2.00 

81 

60 

1.35 

90 

42 

2.12 

99 

78 

1.27 

117 

57 

2.03 

87 

69 

1.26 

60 

33 

1.82 

78 

63 

1.24 

108 

57 

1.90 

81 

60 

1.35 

108 

57 

1.90 

105 

75 

1.40 

96 

48 

2.00 

90 

60 

1.50 

75 

42 

1.79 

93 

78 

1.18 

*  Other  characters  showed  that  these  individuals  were  of  the  other  species  rep- 
resented in  the  table. 


1922]       McDonald:  On  Bala/ntid/ium  coU  and  Ealantidium  suis      253 


TABLE  I — (Continued} 


INDIVIDUALS  FROM  PIG  No.  1 
(Bal.  suis,  with  five  exceptions) 


INDIVIDUALS  FROM  PIG  No.  4 
(Bal.  coli,  with  one  exception) 


Length  in 
microns 

Breadth  in 
microns 

Ratio  of 
length  to 
breadth 

Length  in 
microns 

Breadth  in 
microns 

Ratio  of 
length  to 
breadth 

105 

57 

1.85 

69 

60 

_  JL.15 

99 

57 

1.74 

81 

54 

1.50 

105 

54 

1.95 

87 

66 

1.32 

54 

27 

2.00 

84 

69 

1.22 

57 

30 

1.90 

78 

60 

1.30 

36 

24 

1.50* 

66 

51 

1.29 

81 

31 

2.23 

66 

54 

1.22 

75 

42 

1.78 

96 

66 

1.45 

66 

33 

2.00 

81 

54 

1.50 

78 

36 

2.08 

84 

66 

1.28 

93 

39 

2.39 

114 

87 

1.31 

63 

36 

1.74 

87 

69 

1.26 

102 

48 

2.06 

93 

72 

1.29 

78 

39 

2.00 

84 

72 

1.17 

81 

42 

1.93 

102 

65 

1.58 

87 

48 

1.82 

87 

63 

1.38 

93 

45 

2.03 

99 

66 

1.50 

84 

42 

2.00 

81 

72 

1.13 

81 

39 

2.04 

78 

63 

1.24 

75 

39 

1.93 

102 

75 

1.36 

78 

45 

1.74 

66 

48 

1.38 

75 

37 

2.01 

75 

57 

1.32 

100 

45 

2.11 

84 

66 

1.27 

81 

39 

2.04 

93 

66 

1.40 

72 

39 

1.85 

72 

58 

1.24 

84 

40 

2.06 

96 

72 

1.33 

90 

42 

2.07 

90 

68 

1.32 

78 

36 

2.08 

60 

39 

1.54 

102 

48 

2.06 

87 

69 

1.26 

81 

37 

2.10 

69 

54 

1.28 

66 

37 

1.78 

90 

69 

1.31 

87 

36 

2.41 

69 

54 

1.28 

78 

42 

1.86 

72 

60 

1.20 

84 

42 

2.00 

75 

57 

1.47 

90 

38 

2.37 

75 

62 

1.2X 

66 

35 

1.89 

72 

63 

1.14 

78 

42 

1.86 

90 

75 

1.20 

97 

44 

2.20 

74 

66 

1.12 

79 

37 

2.07 

72 

54 

1.33 

98 

42 

2.32 

60 

50 

1.20 

90 

45 

2.00 

84 

58 

1.45 

87 

49 

1.78 

84 

64 

1.31 

90 

36 

2.50 

88 

60 

1.47 

81. 

35 

2.31 

99 

75 

1.32 

69 

48 

1.44* 

75 

54 

1.39 

*  Other  characters  showed  that  these  individuals  were  of  the  other  species  rep- 
resented in  the  table. 


254 


University  of  California  Publications  in  Zoology       [V°L.  20 


TABLE  I— (Continued} 


INDIVIDUALS  FROM  Pia  No.  1 
(Bal.  suis,  with  five  exceptions) 


INDIVIDUALS  FROM  PIG  No.  4 
(Bal.  coli,  with  one  exception) 


Length  in         Breadth  in 
microns             microns 

Ratio  of 
length  to 
breadth 

90 

54 

1.68 

66 

33 

2.00 

76 

38 

2.00 

78 

42 

1.86 

90 

57 

1.58 

66 

40 

1.65 

81 

39 

2.04 

96 

39 

2.43 

75 

38 

1.98 

84 

39 

2.18 

51 

30 

1.70 

75 

39 

1.92 

84 

40 

2.05 

116 

47 

2.48 

84 

36 

2.32 

81 

39 

2.04 

75 

Aver- 

45 

1.68 

age     86 

43 

1.99 

Length  in 
microns 

Breadth  in 
microns 

Ratio  of 
length  to 
breadth 

81 

69 

1.18 

66 

52 

1.27 

93 

63 

1.48 

81 

75   ' 

1.08 

96 

75 

1.28 

114 

90 

1.27 

75 

60 

1.25 

87 

72 

1.21 

84 

60 

1.40 

87 

63 

1.38 

84 

63 

1.33 

72 

60 

1.20 

90 

66 

1.36 

84 

72 

1.16 

93 

72 

1.29 

87 

58 

1.50 

93 

72 

1.29 

86 


66 


1.30 


While  taking  the  measurements  of  each  individual,  observations  were 
made  regarding  the  position  of  the  mouth,  the  type  and  size  of  macro- 
nucleus,  number  and  location  of  contractile  vacuoles,  and  any  other 
characters  which  might  aid  in  differentiation. 

In  the  handling  of  the  data  on  dimensions  I  have  followed  in  a 
general  way  the  method  used  by  Jennings  (1908)  in  differentiating 
races  of  Paratniaecium.  For  the  purpose  of  this  work,  however,  the 
results  seemed  more  lucid  if,  instead  of  plotting  length  and  breadth 
along  separate  axes,  the  ratio  of  length  to  breadth  was  computed  for 
each  individual  and  if  these  ratios  were  then  plotted  on  the  abscissa 
while  the  numbers  of  individuals  having  each  of  these  ratios  were 
plotted  on  the  ordinate.  In  computing  the  ratios  the  quotient  was 
carried  to  the  second  decimal  place.  But  in  the  construction  of  the 
curves  only  intervals  of  tenths  (or  first  decimal  place)  were  used; 
thus,  for  example,  all  ratios  occurring  between  1.25  and  1.34  inclusive 
were  grouped  as  if  they  were  1.3.  This  had  two  advantages :  first,  it 
produced  a  smoother,  steeper  curve  than  would  result  if  smaller  inter- 
vals were  taken,  using  the  same  number  of  individuals  measured,  and 
emphasized  group  rather  than  individual  variations.  Second,  this 
grouping  reduced  any  error  which  might  result  from  the  observer 
showing  a  preference  for  one  graduation  of  the  micrometer  when 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      255 

an  individual  measured  more  than  one  but  less  than  another  whole 
division  of  the  scale ;  e.g.,  such  a  preference  might  result  in  the  tabu- 
lation of  several  individuals  having  a  length  of  72/t,  and  of  none  with 
a  length  of  7 1/*,,  though  in  reality  all  lay  within  these  two  limits  and 
as  many  were  as  near  to  one  as  to  the  other. 

As  previously  mentioned,  the  graduations  along  the  ordinate 
represent  the  number  of  individuals,  each  small  interval  representing 
one  individual.  In  Jennings'  (1908)  work  these  intervals  represent 
percentages  of  the  total  number  of  individuals.  But  it  happens  that 


I.I       1.2      1.3      1.4      1.5      1.6     1.7       1.8      1.9      2.0      2.1      2.2      2.3      2.4      2.5      2.6 

Fig.  A.  Graphic  representation  of  the  variation  in  the  ratio  of  length  to 
breadth  among  200  Balantidium  chosen  at  random  from  samples  of  material  taken 
from  several  different  pigs.  The  number  of  individuals  is  measured  on  the  ordi- 
nate, the  ratios  on  the  abscissa.  The  dotted  line  is  the  curve  resulting  from  the 
combination  of  the  two  curves  shown  in  figure  B,  superimposed  here  to  facilitate 
comparison. 

in  the  graphs  shown  in  figures  B  and  C,  the  number  of  individuals 
showing  a  certain  ratio  is  identical  with  the  percentage  of  the  total, 
for  in  these  cases  the  total  is  100  individuals. 

Figure  A  represents  graphically  the  result  of  the  first  attempt 
to  determine  the  existence  of  different  types.  Measurements  were 
made  of  200  individuals.  At  least  ten  slides  were  used  in  getting 
these  measurements  and  they  were  prepared  from  samples  taken  from 
nearly  as  many  different  pigs.  It  will  be  noted  that  the  curve  pro- 
duced by  plotting  the  ratios  of  these  individuals  is  decidedly  bimodal. 
One  mode  represents  those  individuals  which  are  approximately  1.2 
times  as  long  as  wide,  while  the  other  represents  those  which  are  1.6 
to  1.8  times  as  long  as  wide. 

These  findings  seemed  to  fully  justify  my  early  suspicions  that 
there  were  two  very  different  types  of  balantidia  parasitic  in  pigs. 


256 


University  of  California  Publications  in  Zoology       [VOL.  20 


But  it  was  decided  to  conduct  one  more  experiment,  for  corroboration, 
under  slightly  different  conditions  and  with  especial  care  in  fixation 
of  the  material.  It  had  been  noted  that  though  often  both  types 
occurred  in  the  same  pig  (which  was  the  case  in  most  of  the  samples 
used  in  the  first  measurements),  still  one  type  might  be  greatly  in 
excess,  or  there  might  be  only  one  type  present.  In  getting  material 


1.1       1.2      1.3      1.4      1.5      1.6     1.7      1.8      1.9       2.0      2.1 


2.2      2.3      2.4       2.5      2.6 


Fig.  B.  Graphic  representation  of  the  difference  in  ratio  of  length  to  breadth 
between  two  carefully  selected  lots,  of  100  individuals  each,  of  Balantidium  from 
separate  hosts.  The  continuous  line  represents  those  from  one  pig  (nearly  all  are 
Balantidium  coli)  ;  the  broken  line,  those  from  the  other  pig  (nearly  pure  infection 
with  Balantidium  suis). 

Fig.  C.  This  graph  shows  the  variation  in  the  ratio  of  length  to  breadth  among 
100  Balantidium  secured  from  a  case  of  balantidiasis  in  man. 

for  this  second  set  of  measurements,  it  seemed  best  to  take  it  from  pigs 
which  had,  as  nearly  as  could  be  determined,  pure  infections  of  the 
respective  types.  Fortunately  these  requirements  were  fulfilled  in 
the  next  lot  of  pigs  examined.  Both  samples  of  material,  the  one  con- 
taining the  ovoid  and  the  one  containing  the  elongate  type,  were 
treated  in  exactly  the  same  way.  They  were  killed  at  the  same  time 


1922]       McDonald:  On  Balantidium  eoli  and  Balantidium  suis      257 

with  the  same  fluid  (in  separate  containers)  and  in  the  same  water 
bath.  Thence  to  70  per  cent  alcohol  the  treatment  continued  identical. 
One  hundred  individuals  from  each  sample  of  material  were  measured. 

From  these  measurements  the  graphs  shown  in  figure  B  were  con- 
structed in  the  same  manner  as  the  preyious  one,  except"  that  the 
curves  of  the  separate  samples  were  plotted  separately  on  the  same 
axis.  The  continuous  line  represents  the  individuals  from  one  pig  and 
the  broken  line  those  from  the  other.  The  mode  of  the  first  curve 
occurs  at  1.3.  If  the  ratios  1.2  and  1.4  be  included  with  1.3,  it  is  found 
that  80  per  cent  came  within  these  limits.  Of  the  entire  number  of 
individuals  in  the  lot  only  one  showed  a  ratio  of  1.6  and  one  as  high 
as  1.7,  while  there  were  none  with  a  higher  ratio.  The  second  curve 
reaches  its  highest  point  at  2.0,  while  71  per  cent  of  the  entire  number 
measured  is  included  between  1.8  and  2.2.  A  number  of  individuals 
have  ratios  above  2.2,  while  one  had  a  ratio  as  great  as  2.7.  Five  indi- 
viduals have  ratios  below  1.6,  at  which  point  the  curves  begin  to  over- 
lap ;  but  in  practically  every  one  of  these  individuals  there  were 
observed  characters  (which  are  discussed  below)  that  made  it  quite 
evident  that  they  were  really  of  the  type  represented  by  the  other 
curve. 

Upon  comparing  figures  A  and  B  their  likeness  is  very  striking, 
the  second  being  corroborative  of  the  results  shown  by  the  first.  That 
both  are  bimodal  is  evident.  However,  the  low  points,  the  point  of 
demarcation  of  the  two  groups,  do  not  occur  at  the  same  place ; 
in  the  first  it  is  at  1.4,  while  in  the  second  it  occurs  at  1.6.  Also  the 
median  of  the  first  mode  in  figure  A  occurs  at  1.2  while  in  figure  B 
it  is  at  1.3,  and  the  median  of  the  second  mode  in  figure  A  is  at  1.7 
while  in  figure  B  it  occurs  at  2.0 ;  that  is,  in  figure  A  the  entire  curve 
is  shifted  to  the  left,  meaning  that  all  ratios  are  decreased  or  that  all 
individuals  approach  nearer  to  the  spherical  shape.  This  shifting  is 
greatest  in  the  case  of  the  second  mode.  This  in  conjunction  with 
the  greatest  breadth  of  the  second  curve  in  figure  B  is  what  would 
be  expected  if  the  premise  in  regard  to  the  effect  of  fixation  discussed 
above  (page  251)  is  correct.  Extra  care  was  used  in  the  fixation  of 
the  latter  lot  of  material  whereas  in  the  former  only  the  ordinary  pre- 
cautions were  taken.  At  any  rate  these  differences  between  the  two 
groups  do  not  detract  from  the  evidence  which  they  offer  that  there 
are  two  distinct  types  of  balantidia  parasitic  in  pigs. 

The  value  of  these  curves  in  showing  race  or  species  differentiation 
is  directly  proportional  to  the  extent  to  which  any  other  factors  which 


258  University  of  California  Publications  in  Zoology       [VOL.  20 

might  produce  a  bimodal  curve  are  non-operative.  Factors  involved 
in  faulty  technique  were  eliminated  as  far  as  possible.  Over  the  effect 
of  growth  or  age  variation,  however,  the  observer  has  no  control.  The 
possibility  of  these  variations  producing  such  curves  as  the  one  above 
is  precluded  by  reference  to  the  data  from  which  the  curves  are  con- 
structed. Among  the  individual  measurements  recorded  in  Table  I 
it  will  be  noted  that  there  are  small  individuals  measuring  27  X  50/x, 
and  others  measuring  42  X  50/x;  and  that  among  the  larger  individ- 
uals, some  measure  50  X  120/*,  and  some,  90  X  150/x.  Further  study 
of  Table  I  shows  that  the  two  types  are  found  among  all  sizes  of 
individuals;  consequently  the  variation  of  body  proportions  repre- 
sented by  the  graphs  is  not  correlated  with  variations  of  size,  and 
probably  not  with  the  age  or  growth  of  the  individuals. 

That  the  variation  could  be  accounted  for  by  the  occurrence  of 
fission  seems  unlikely.  Individuals  might  continue  to  elongate  until 
binary  fission  occurred,  and  then  by  this  process  they  might  be 
shortened  and  the  body  proportion  changed.  Two  considerations 
oppose  this  explanation.  In  figure  A  nearly  equal  numbers  are  of  the 
respective  types;  in  figure  B  each  example  contained  almost  exclusively 
one  type  of  individual.  In  the  former  material  very  few  dividing 
individuals  were  found,  while  in  the  latter  not  a  single  individual  was 
seen  in  fission  in  either  sample  of  material.  But  to  accord  with  the 
above  explanation  one  would  expect  to  find  many  dividing  forms 
among  the  elongate  individuals  represented  by  the  broken  line.  In 
the  second  place,  if  this  explanation  were  valid  one  would  expect 
curves  showing  variation  of  body  proportions  to  be  continuous.  Such 
is  not  the  case,  as  is  shown  in  figures  A  and  B  where  the  curve  is 
bimodal  due  to  a  decided  decrease  of  individuals  having  proportions 
intermediate  between  the  two  types. 

The  possibility  of  any  effect  from  gametic  variation,  was  eliminated 
by  the  study  of  conjugating  forms,  through  which  it  was  determined 
that  isogamy  was  the  rule.  Likewise  the  possibility  of  influence  of 
the  quality  of  intestinal  content  of  the  host  was  eliminated  by  the 
frequent  occurrence  of  both  types  in  the  same  host.  Other  factors  it 
would  seem  must  be  of  minor  importance  and  should  give  way  for 
more  positively  corroborative  evidence  which  may  be  found  in  cor- 
related morphological  difference. 

Other  specific  characters. — In  addition  to  the  differences  in  relative 
lengths  of  the  axes,  one  notes  a  distinct  difference  in  the  points  of 
intersection,  due  to  the  variation  in  the  shape  of  the  types  as  pictured 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      259 


in  figures  D,  E,  F,  G,  and  H.  The  one  form  resembles  very  closely 
a  hen's  egg,  the  small  end  being  anterior.  In  this  case  the  longest 
diameter  crosses  posterior  to  the  midpoint  of  the  longitudinal  axis. 
In  the  elongate  type,  usually  the  posterior  end  is  as  much  drawn  to 


Figs.   D-H.     Camera  lucicla  drawings  of  Balantidium  suis  sp.  nov.    (figs.   D 
and  E),  and  Balantidium  coli  (figs.  F,  G,  and  H),  showing  specific  differences. 

a  point  as  is  the  anterior,  and  often  more  so.  In  these  cases  the  longest 
diameter  intersects  the  longitudinal  axis  at  or  anterior  to  its  midpoint. 
Coincident  with  the  taking  of  measurements  a  careful  search  was 
made  to  detect  other  morphological  differences  which  might  occur 
between  the  two  forms  and  be  of  aid  in  distinguishing  one  from  the 
other.  The  earliest  difference  to  be  noted  related  to  the  macronucleus. 
The  macronucleus  in  the  ovoid  type  is  relatively  short,  being  approxi- 
mately !/3  the  length  of  the  entire  organism.  It  is  customarily  bean- 
shaped  in  appearance,  but  may  be  almost  straight  or  so  sharply  bent 


260  University  of  California  Publications  in  Zoology       [V°L.  20 

at  its  middle  as  to  form  a  short  V  (fig.  I),  and  its  width  averages  about 
0.4  to  0.5  of  its  length.  In.  the  slender  types  the  macronucleus  is  rela- 
tively long  and  slender,  being  approximately  %  of  the  entire  length 
of  the  organism.  It  is  ordinarily  sausage-shaped,  but  it  may  also  be 
in  the  form  of  a  straight  rod  slightly  enlarged  toward  the  ends,  or 
it  may  be  so  curved  as  to  form  an  almost  complete  ring.  In  contrast 
to  the  form  described  above,  the  width  in  this  case  is  about  0.2  to  0.3 
of  its  length.  Differences  so  great  as  these,  viz.,  a  length  2  to  3  times 
the  breadth  in  one  case  and  4  to  5  times  the  breadth  in  the  other  are 
easily  recognizable  without  actual  measurement.  These  figures  rep- 
resent the  average  and  do  not  mean  that  the  limits  of  the  two  never 
overlap.  This  difference  in  nuclei  serves  as  one  of  the  easiest  and 
surest  ways  of  distinguishing  the  two  types,  for  though  the  organism 
during  locomotion  may  modify  its  proportions  tremendously  this  does 
not  noticeably  affect  the  nucleus.  It  has  been  impossible  to  determine 
any  difference  between  the  micronuclei  of  the  two  types. 

A  very  noticeable  difference  concerns  the  relative  position  of  the 
cytostome.  In  the  ovoid  type  the  cytostome  is  almost,  though  never 
quite,  terminal  (see  figs.  F,  G,  and  H).  As  mentioned  previously,  the 
anterior  end  is  ordinarily  drawn  out  to  form  a  fairly  decided  point 
which  lies  within  the  area  enclosed  by  the  adoral  cilia.  In  the  slender 
type  the  cytostome  is  more  laterally  placed.  The  posterior  limit  of  the 
right  lip  of  the  cytostome  may  extend  ventrally  to  a  point  %  of  the 
length  of  the  animal,  in  which  case  the  dorsal  portion  of  the  adoral 
circlet  of  cilia  may  pass  approximately  through  the  terminal  point 
of  the  body,  but  in  normal  form  this  point  will  never  be  within  the 
adoral  area.  The  parts  which  make  up  the  adoral  region  of  the 
animals  show  no  fundamental  differences  except  variation  in  the  rela- 
tive position  of  parts  due  to  the  lateral  displacement  of  the  cytostome. 
For  example,  the  plane  of  demarcation  between  ectoplasm  and  endo- 
plasm,  which  is  approximately  vertical  to  the  long  axis  of  the  animal 
in  the  ovoid  form,  is  at  a  decided  angle,  the  ventral  edge  lying  farther 
posterior  in  the  elongate  forms  (see  figs.  D  and  E). 

In  the  opinion  of  some  authors  the  ventral  displacement  of  the 
mouth  is  very  significant  (Delage  and  Herouard,  1896;  Minchin, 
1912).  These  authors  believe  that  the  ventral  displacement  of  the 
cytostome  is  progressive  with  evolution  of  the  organism;  i.e.,  that  in 
the  more  primitive  types  the  cytostome  is  terminal  while  in  advanced 
groups  it  is  successively  displaced  farther  ventrally.  Viewed  in  this 
light,  the  position  of  the  mouth  is  here  of  considerable  significance  as 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      261 

a  specific  character.  Attempts  to  discriminate  between  the  two  forms 
on  the  basis  of  cytopyge  or  vacuoles  were  without  result. 

The  specific  differences  just  discussed  have  seemed  to  indicate  a 
sufficient  degree  of  separation  of  the  two  types  to  warrant  iho~ division 
of  the  ciliates  of  the  genus  Balantidium  which  occur  in  the  pig  into 
two  distinct  species.  The  description  by  Malmsten  (1857),  in  con- 
junction with  the  figures  (Malmsten,  pi.  1,  figs.  1-6)  which  he  pub- 
lished, make  it  practically  certain  that  the  ovoid  type  is  the  one 
originally  described  by  him  and  to  which  he  gave  the  name  Para- 
moecium  (?)  coli. 

So  far  as  I  have  been  able  to  determine,  the  elongate  species  above 
described  has  never  before  been  distinguished  from  Balantidium  coli. 
For  this  new  species  I  suggest  the  name  Balantidium  suis.  As  a  sum- 
mary of  the  specific  characters  discussed  above  I  give  the  following 
description : 

Balantidium  suis  sp.  nov. — Body  elongate;  length  approximately 
twice  the  breadth  and  varies  from  35  to  120/* ;  breadth  from  20  to  60/x ; 
usually  tapers  more  posteriorly,  is  blunter  anteriorly,  longest  diameter 
transects  longitudinal  axis  anterior  to  its  midpoint ;  adoral  region  ven- 
trally  placed,  cytostome  %  of  way  posteriorly  along  ventral  surface; 
nucleus  rod  or  sausage-shaped,  at  least  one-half  the  length  of  the  entire 
organism,  its  width  about  one-fourth  of  its  length ;  the  species  is  para- 
sitic in  the  pig. 

The  specific  name,  Balantidium  suis,  seemed  fitting  since  it  indi- 
cated the  common  host,  Su$  scrofa.  Whether  or  not  this  species  occurs 
in  man  it  has  not  been  possible  to  determine  conclusively.  A  review 
of  published  case  records  of  balantidiasis  seems  to  show  that  it  does 
not,  but  only  a  few  of  these  records  are  accompanied  by  figures  or 
descriptions  of  the  organisms  which  are  adequate  for  making  positive 
discrimination.  Fortunately,  I  have  been  able  in  two  cases  to  make 
some  direct  observations. 

Through  the  kindness  of  Mr.  W.  H.  Barnes,  of  the  Department  of 
Pathology  of  the  University  of  California,  I  was  permitted  to  study 
sections  of  the  human  intestine  which  he  had  obtained  at  an  autopsy 
following  a  fatal  attack  of  balantidiasis.  Imbedded  in  the  serous  and 
subserous  layers  were  numerous  balantidia.  Measurements  to  show 
proportions  were  of  little  value  under  the  conditions,  for  the  form 
of  each  organism  was  largely  determined  by  pressure,  exerted  by  sur- 
rounding tissues.  But  from  other  characters,  the  type  of  nucleus 
especially,  it  was  conclusively  determined  that  the  species  there  present 
was  Balantidium  coli.  No  individuals  of  Balantidium  suis  were  found. 


262  University  of  California  Publications  in  Zoology       [VOL.  20 

Measurements  of  balantidia  as  they  occur  free  in  the  human  intes- 
tine were  made  possible  through  the  kindness  of  Dr.  E.  L.  Walker, 
of  the  Hooper  Institute  of  Medical  Research,  who  loaned  me  several 
slides  which  he  had  prepared  while  in  the  Philippine  Islands.  This 
material  had  been  stained  with  haematoxylin.  Using  the  same  pre- 
cautions as  in  previous  work,  a  total  of  100  individuals  was  measured. 
The  data  were  handled  as  before  and  the  resulting  graph  is  shown  in 
figure  C.  In  comparison  with  previous  graphs  it  will  be  noted  that 
this  graph  closely  approaches  coincidence  with  the  curves  representing 
Balantidium  coli,  for  its  mode  is  at  1.3  while  the  extreme  portion  of 
length  and  breadth  is  1.5. 

In  addition  to  slides  of  human  material,  there  was  also  loaned 
material  from  one  pig  and  from  one  monkey.  It  is  interesting  that 
each  showed  a  pure  infection  with  Balantidium  coli.  The  monkey 
(Monkey  No.  10,  Table  I;  Walker,  1913)  had  been  experimentally 
infected  by  feeding  it  cysts  from  a  pig,  but  not  the  pig  from  which 
the  above-mentioned  material  was  taken.  Therefore  this  material 
yields  no  evidence  regarding  the  validity  of  the  specific  differentiation 
nor  the  possibility  of  Balantidium  suis  becoming  established  in  mon- 
keys or  in  man. 

There  is  no  likelihood  of  confusing  the  new  species,  Balantidium 
suis  with  Balantidium  minutum  (Schaudinn,  1899).  The  differences 
are  very  marked.  The  body  of  the  latter  is  oval,  pointed  anteriorly, 
more  like  Balantidium  coli.  The  peristome  reaches  to  the  equatorial 
plane.  There  is  but  a  single  vacuole  while  there  are  two  in  each  of 
the  species  considered  here.  The  macronucleus  is  spherical,  whereas 
it  is  elongate  in  both  Balantidium  coli  and  Balantidium  suis. 


MORPHOLOGY 

Balantidium  coli  (Malmsten)  and  Balantidium  suis  sp  nov.  are 
ciliated  protozoans,  barely  visible  to  the  unaided  eye,  and  are  in  a 
general  way  sac-shape  (balantidium,  little  bag).  Viewed  through  the 
microscope  they  appear  grayish  green  in  color.  The  homogeneity  of 
the  cell  contents  is  broken  by  the  presence  of  the  nuclei,  the  contractile 
vacuoles,  the  food  vacuoles,  and  sometimes  by  the  presence  of  highly 
refractile  bodies,  the  paramylum  bodies.  The  entire  surface  of  the 
body,  except  that  of  the  oral  plug,  is  covered  with  fine  cilia.  The  cell 
contents  are  retained  by  a  thin  transparent  pellicle  which  is  protective 


1922]      McDonald:  On  Balantidium  coU  and  Balantidium  suis      263 

in  function.  The  cytoplasm  is  distinctly  differentiated  into  ectoplasm 
and  endoplasm.  The  former  constitutes  a  thin  layer  just  underneath 
the  pellicle  and  in  it  is  situated  the  basal  apparatus  of  the  cilia.  The 
layer  of  ectoplasm  thickens  greatly  at  the  anterior  end  of  the  animal, 
to  form,  as  it  were,  a  matrix  for  the  cytostome  and  its  accessory  appa- 
ratus. Within  the  ectoplasm,  but  not  set  off  from  it  by  a  sharp  line 
of  demarcation,  is  the  endoplasm.  In  the  endoplasm  are  numerous 
food  inclusions,  often  present  in  the  form,  of  starch  or  paramylum 
bodies.  The  macronucleus  and  the  micronucleus  are  also  within  it, 
but  seem  to  have  no  constant  position  in  the  cell.  The  .macronucleus 
is  either  bean-shaped  (as  in  Balantidium  coli)  or  elongate  and  sausage- 
shaped  (as  in  Balantidium  suis).  There  are  two  contractile  vacuoles, 
the  larger  being  situated  anteriorly  and  the  smaller  posteriorly.  They 
lie  closely  beneath  or  may  be  entirely  surrounded  by  ectoplasm,  thus 
belonging  really  within  that  layer. 

So  far  as  can  be  determined  the  animals  show  no  modification  with 
respect  to  a  substratum,  yet  the  lateral  and  posterior  displacement  of 
the  cytostome  has  lead  to  the  designation  of  that  side,  toward  which 
displacement  occurs,  as  ventral,  and  the  opposite  surface  as  dorsal. 
This  terminology  is  very  nearly  universal  in  the  literature  on  Balan- 
tidium, and  the  correlated  terms  of  right  and  left  are  used  in  the 
original  description  of  the  family  Bursaridae  (Stein,  1867)  and  the 
genus  Balantidium  (Claparede  and  Lachmann,  1858).  The  dorsal 
side  may  be  somewhat  more  convex  than  the  ventral ;  this  occurs  not 
infrequently  in  Balantidium  suis,  though,  due  to  the  plasticity  of  the 
organism,  this  is  by  no  means  constant.  No  part  of  the  body  is  differ- 
entiated for  skeletal  purposes.  The  anal  aperture  or  cytopyge  is  at 
the  posterior  tip  and  may  be  present  as  an  actual  aperture  or  only 
as  an  extreme  thinning  of  the  ectoplasm  and  pellicle  at  this  point.  In 
connection  with  it  there  is  usually  a  rectal  vacuole  which  serves  as  a 
storage  reservoir  for  solid  waste  awaiting  extrusion. 


ECTOPLASMIC  STRUCTURES 

Pellicle. — The  entire  body  is  covered  by  an  extremely  thin  but 
resistant  pellicle  (pel.,  figs.  I  and  L).  The  pellicle  seems  to  be  some- 
what thickened,  as  shown  by  a  higher  degree  of  refractibility,  along 
the  margin  of  the  lips  of  the  cytostome  where  it  turns  in  to  form  the 
lining  of  the  oesophagus  and  the  groove  in  which  the  oral  cilia  are  set ; 
otherwise,  it  is  nowhere  noticeably  specialized.  It  shows  alternating 


264 


University  of  California  Publications  in  Zoology       EV°L.  20 


post.  c.  v 


Pig.  I.  Balantidium  ooli.  Ventral  view  showing  principal  structures.  The 
adoral  cilia,  with  exception  of  one  at  either  side,  are  indicated  by  basal  granules 
only.  The  adoral  membranelles  are  also  represented  solely  by  the  basal  apparatus. 
Ectoplasm  is  shaded,  and  ciliary  rootlets  are  shown  on  one  side  only.  X  1250. 
ad.  oil.,  adoral  cilia;  ad.  cil.  /.,  adoral  ciliary  fiber;  ad.  mcmb.,  adoral  membranelles; 
ant.  c.  v.,  anterior  contractile  vacuole;  bg.,  basal  granule;  bg.  ad.  cil.,  basal  granules 
of  adoral  cilia ;  cil.,  cilia ;  oil.  r.,  ciliary  rootlet ;  dr.  oes.  /.,  circumoesophageal  fiber ; 
cytpg.,  eytopyge ;  ect.,  ectoplasm ;  enl.  ad.  cil.  r.,  enlargement  of  adoral  ciliary  root- 
let; end.,  endoplasm;  gr.  b.,  granular  band  of  ectoplasm;  long.  /.,  longitudinal 
fibers;  moo.,  macronucleus ;  mic.,  micronucleus ;  mot.,  motorium;  nuc.memb., 
nuclear  membrane;  oes.,  oesophagus;  or.pl.,  oral  plug;  or.pl.f.,  oral  plug  fibers; 
pel.,  pellicle ;  per.,  margin  of  peristome ;  post.  c.  v.,  posterior  contractile  vacuole ; 
rad.  /.,  radial  fiber ;  ret.  v^  rectal  vacuole. 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      265 

ridges  and  grooves,  the  cilia  passing  through  the  bottom  of  the  latter, 
but  this  condition  is  not  due  to  longitudinal  thickenings  in  the  pellicle 
itself,  but  to  the  fact  that  it  is  closely  applied  to  the  ectoplasm  which 
is  thus  furrowed.  It  can  often  be  separated  in  "  blisters  'J_  from  the 
ectoplasm  by  tannic  acid  or  weak  alcohol,  and  when  thus  removed  it 
shows  regular  longitudinal  rows  of  perforations  through  which  the 
cilia  pass  out  from  the  ectoplasm.  In  this  condition  its  transparency 
is  very  evident.  The  pellicle  is  not  extremely  impervious.  For 
instance,  when  the  active  animals  are  introduced  into  normal  salt 

ad.  memb.   „_ 

cyst. 


dr.  oes.  f. II / 


or.  pi.  f. 


per. 


Fig.  J.  The  neuromotor  apparatus  of  the  adoral  region,  anterior  view.  X  2000. 
.,  adoral  ciliary  fiber;  ad.  memb.,  adoral  membranelles ;  ~bg.ad.cil.,  basal 
granule  of  adoral  eilia;  dr.  oes.  f.,  circumoesophageal  fiber;  oytst.,  cytostome; 
mot.,  motorium;  or.pl.,  oral  plug;  or.  pi.  f.,  oral  plug  fibers;  per.,  margin  of  peri- 
stome. 

solution  plasmolysis  takes  place  very  quickly,  and  they  present  a 
grotesque  appearance  as  they  swim  about  with  several  huge  depres- 
sions in  their  surfaces  due  to  the  shrinkage.  Intra  vitam  stains  such 
as  neutral  red  and  Janus  green  also  penetrate  very  quickly.  Resist- 
ance to  pressure  and  mechanical  change,  however,  is  very  marked,  and 
is  due  to  its  tenacity  and  flexibility,  both  of  which  qualities  are  shown 
when  the  animal  forces  itself  through  an  opening  much  smaller  than 
the  normal  diameter  of  its  body  (fig.  K)  and  also  by  the  extreme  flat- 
tening which  it  withstands  under  the  increasing  pressure  of  the  cover- 
glass  when  evaporation  of  the  preparation  is  allowed.  As  previously 
mentioned,  these  qualities  indicate  that  the  pellicle  is  protective  and 
retentive  in  function  rather  than  supportive  or  skeletal. 


266  University  of  California  Publications  in  Zoology       [V°L-  20 

These  organisms  show  remarkable  mobility  when  observed  under 
conditions  as  nearly  normal  as  possible.  I  have  attempted  to  depict 
something  of  this  plasticity  in  figure  K.  As  they  travel  amid  the 
debris  in  the  intestinal  contents,  which  has  been  removed  with 
them,  a  tendency  to  penetrate  is  much  more  noticeable  than  any 
avoiding  reaction.  Instead  of  reversing  the  ciliary  action,  backing 
away  and  taking  a  new  direction  as  would  paramaecia,  the  balantidia, 
when  they  come  in  contact  with  a  solid  object,  rather  appty  themselves 
to  the  surface,  round  up,  and  seem  to  roll  along  it.  After  a  moment 
of  such  slow  contortion,  they  may  swim  away  in  a  new  direction, 


Fig.  K.     Diagrammatic  illustration  of  the  plasticity  of  the  organism,  resulting 
in  ability  to  pass  through  remarkably  small  openings. 

determined  by  the  direction  of  the  anterior  end.  They  avail  them- 
selves of  the  slightest  opportunity  to  force  their  way  through  or 
between  any  obstacles.  The  anterior  end,  especially  the  thickened 
ectoplasmic  portion,  becomes  at  such  times  decidedly  elongate  and 
conical  (fig.  K,  6).  The  cilia  of  this  region  beat  spirally  producing  a 
boring  action  as  this  anterior  tip  is  protruded  into  any  slight  opening. 
This  action  has  in  many  instances  been  observed  to  cause  two  obstacles, 
either  of  which  was  larger  than  the  organism  itself,  to  separate 
sufficiently  to  allow  it  to  pass  between.  The  aperture  need  not  be 
one-half  of  the  diameter  of  the  animal  for  the  latter  will  constrict 
(fig.  K,  c)  and  the  fluid  contents  flow  through  anteriorly  as  it 
progresses,  resembling  the  process  of  putting  a  bag  of  beans  through 
a  small  hole  in  a  board.  Throughout  observations  of  the  activity  of 
these  organisms,  one  is  impressed  with  their  fitness  for  penetrating 
the  mucous  lining  of  the  intestine  and  the  underlying  tissues.  Its 
thigmotropic  response,  its  boring  action,  and  its  extreme  plasticity, 
all  seem  to  be  adaptations  for  the  function  of  penetration. 

Ectoplasm. — Immediately  underneath  the  pellicle,  the  cytoplasm 
is  differentiated  to  form  the  ectoplasm  (ect.,  fig.  I;  pi.  27,  figs.  1-7). 
The  ectoplasmic  layer,  except  at  the  anterior  end,  does  not  exceed  two 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      267 

microns  in  thickness.  The  anterior  end  of  the  animal,  that  is,  all 
anterior  to  a  transverse  plane  which  would  transect  the  body  at  a 
point  %  to  y5  of  the  way  to  the  posterior  end,  is  composed  entirely 
of  ectoplasm.  In  this  cone-shaped  area  is  located  the  cytostome  and 
a  large  part  of  the  neuromotor  apparatus.  The  protoplasniTof  this 
region  seems  to  be  homogeneously  granular  in  fundamental  structure.. 
It  stains  very  deeply  with  haematoxylin ;  so  deeply  in  fact,  that  in 
differentiation  it  is  necessary  to  destain  other  parts  of  the  body  almost 
completely  before  this  part  reaches  a  degree  of  transparency  suitable 
for  study.  With  Mallory's  connective  tissue  stain  this  region  also 
stains  very  densely,  taking  on  both  the  brilliant  red  and  the  deep  blue 
elements  of  the  stain,  in  different  structures,  as  will  be  explained  below. 
This  extensive  thickening  of  the  ectoplasm  at  the  anterior  end  is  clearly 
shown  in  the  figures  by  Leuckart  (1861)  and  has  been  noted  by  nearly 
all  who  have  studied  the  animal  more  recently,  but  I  have  failed  to 
find  any  discussion  of  its  significance.  This  same  phenomenon  occurs 
in  the  Ophyroscolecidae,  as  pointed  out  by  Sharp  (1914)  in  his  work 
on  Diplodinium  and  by  Braune  (1913)  in  Ophyroscolex.  In  these 
cases  the  change  seems  to  be  correlated  with  the  high  degree  of  activity 
and  specialization  of  the  anterior  end  of  the  animal ;  in  Diplodinium 
in  connection  with  its  selective  feeding,  and  in  Balantidium  in  con- 
nection with  both  feeding  and  activity  of  this  entire  region  in  pene- 
trating the  mucosa  of  the  intestine.  The  centering  of  the  neuromotor 
apparatus  in  this  region  gives  additional  evidence  in  regard  to  this 
question  which  will  .be  discussed  further  in  connection  with  the  de- 
scription of  that  apparatus. 

Throughout  the  entire  investigation  of  the  minute  structure  of  this 
animal,  I  have  been  unable  to  demonstrate  the  presence  of  any  definite 
plane  of  demarcation  between  endoplasm  and  ectoplasm,  such  as  the 
" ectoplasmic  boundary  layer"  described  by  Sharp  (1914)  in  Diplo- 
dinium, and  shown  in  plate  IV,  figure  3  of  his  paper.  Many  of  the 
fixed  preparations  used  in  the  search  for  such  a  layer  were  sections 
of  the  animal,  treated  as  nearly  as  possible  according  to  the  technique 
used  by  him  and  stained,  as  were  his  preparations,  with  Mallory  's  con- 
nective tissue  stain.  So  far  as  it  was  possible  for  me  to  determine, 
any  sharp  boundary  line  between  ecto-  and  endoplasm  is  lacking.  On 
the  contrary,  they  merge  into  one  another  and  only  in  a  general  way 
can  it  be  said  where  one  terminates  and  the  other  begins. 

Prowazek  (1913,  fig.  2)  describes,  in  Balantidium  coll,  "ein  Art 
von  Zwischenmembran "  which  appears  as  wavy  lines  in  optical  sec- 


268  University  of  California  Publications  in  Zoology       [VOL.  20 

tion.  According  to  his  interpretation  this  "Querlinie"  separates  the 
protoplasm  of  the  cell  body  into  two  regions,  the  *  *  apical  zone, ' '  which 
I  have  described  above  as  a  thickening  of  the  ectoplasm,  and  the  rest 
of  the  cell  protoplasm.  The  extent  of  this  *  *  Zwischenmembran "  he 
does  not  note,  but  his  text  figures  (1  and  2)  do  not  show  it  as  extending 
quite  to  the  pellicle,  but  instead  as  stopping  short  of  the  pellicle  at  a 
distance  about  equivalent  to  the  thickness  of  the  ectoplasm  at  that 
point.  This  is  significant  in  my  interpretation  of  this  region,  namely, 
that  what  appears  as  a  continuous  line  or  plane  when  viewed  from 
the  side  is  in  reality,  as  shown  in  cross-sections  (pi.  27,  figs.  6  and  7), 
a  set  of  diverging  fibers.  These  fibers  take  origin  from  dark-staining 


oil 


cil.  r. 

end. 

Fig.  L.  Portion  of  the  peripheral  region  of  a  cross-section  of  Balantidium  coli, 
showing  the  structure  of  the  ectoplasm  and  arrangement  of  cilia,  somewhat  dia- 
grammatic. X  1500.  b.  ff.,  basal  granule;  oil.,  body-cilia;  oil.r.,  ciliary  rootlet; 
end.,  endoplasm;  gr.  &.,  granular  band  of  ectoplasm;  hy.  &.,  hyaline  band  of  ecto- 
plasm; pel.,  pellicle. 

enlargements  on  the  longitudinal  fibers  in  the  wall  of  the  gullet  and, 
diverging,  pass  peripherally  until  they  turn  posteriorly  at  the  very 
inner  edge  of  the  thin  layer  of  ectoplasm  which  covers  the  remainder 
of  the  body  (pi.  28,  figs.  9-12).  Even  in  lateral  view  careful  focusing 
will  often  show  that  the  apparent ' '  membrane ' '  is  really  discontinuous, 
showing  breaks  and  irregularities  as  one  focuses  on  different  levels 
and  hence  can  not  be  considered  as  a  true  membrane.  The  arrange- 
ment of  these  fibers  will  be  described  more  exactly  under  the  discussion 
of  the  neuromotor  apparatus. 

The  ectoplasm  which  constitutes  a  layer  less  than  3  microns  in 
thickness  around  the  remainder  of  the  periphery  of  the  cell  shows 
a  definite  and  somewhat  complex  structure.  In  tangential  sections 
of  the  surface,  which  are  so  thin  that  they  do  not  include  much  of  the 
underlying  endoplasm,  one  detects  alternating  light  and  dark  longi- 
tudinal spiral  bands  (gr.b.,  hy.b.,  fig.  N).  These  bands  are  parallel 
to  the  rows  of  cilia  and  very  nearly  equal  in  width.  In  cross-sections 
(fig.  L)  they  are  seen  to  extend  nearly,  if  not  quite  the  full  depth  of 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      269 

the  ectoplasm.  As  one  follows  these  bands  (or  "stripes,"  as  they  are 
named  by  Johnson  (1893,  in  his  work  on  8  tent  or)  anteriorly  they  seem 
to  lose  their  distinctness  when  they  become  continuous  with  the  apical 
cone.  In  some  individuals,  however,  one  can  follow  them  some  distance 
into  this  cone,  but  never  is  there  the  same  degree  of  differentiation  of 
the  two  areas  in  this  region. 

In  the  living  animals,  which  are  often  quite  opaque  due  to  inclu- 
sions, it  is  nearly  impossible  to  distinguish  these  longitudinal  light  and 
dark  bands.  With  neutral  red  the  dark  or  granular  band  stains 
faintly.  With  the  haematoxylin  stains  used  in  thin  sections  of  fixed 
material  the  dark  band  seemed  to  be  finely  granular  in  fundamental 
structure.  The  granularity  in  this  case  must  be  determined  largely 
by  the  general  appearance  and  stainability,  for  the  individual  granules 
are  so  small  as  to  defy  identification.  There  is  no  indication,  however, 
of  alveolar  structure,  so  that  the  term  granular  is  probably  the  more 
applicable  and  will  be  used  to  distinguish  this  from  the  light  band. 
The  latter  takes  only  faintly  the  stains  used  and  seems  hyaline  in 
structure.  The  granular  bands  lie  directly  beneath  the  ridges  in  the 
cuticle  which  occur  between  the  rows  of  cilia.  Or  more  correctly, 
the  ridges  on  the  surface  of  the  animal  are  produced  by  the  projection 
of  these  granular  bands  outwardly  beyond  the  hyaline  bands.  These 
latter  are  directly  beneath  the  grooves  of  the  surface  where  the  cilia 
pass  through  the  cuticle  and  attach  with  the  basal  granules  which  lie 
in  longitudinal  rows;  a  single  row  in  each  hyaline  band.  The  ciliary 
rootlets  (cil.  r.,  figs.  I  and  L)  extending  in  from  the  basal  granules 
proceed  diagonally  inward  and  pass  into  the  interior  margin  of  the 
granular  band. 

Stein  as  early  as  1876  pointed  out  these  alternating  dark  and  light 
stripes  in  Stentor.  To  the  granular  and  bright  stripes,  Biitschli 
(1889)  gave  the  names  ' '  Riffenstreif en "  and  "  Zwischenstreif en, " 
respectively.  Johnson  (1893)  gives  a  careful  description  of  these 
bands  as  they  occur  in  Stentor  coeruleus.  He  notes  that  they  vary 
greatly  in  width,  and  this  is  true  in  Balantidium;  but  both  bands  are 
much  narrower  than  in  Stentor,  the  combined  width  of  the  two  not 
exceeding  two  microns.  In  Stentor  coeruleus  Johnson  (1893)  gives 
the  width  of  the  granular  band  as  22/x  and  that  of  the  bright  band 
as  7/x,  these  measurements  being  taken  just  under  the  adoral  zone.  It 
is  interesting  to  note  that  in  Balantidium  coli  the  granular  band  is  also 
slightly  wider  than  the  bright  band.  These  bands  become  narrower 
from  the  region  of  the  greatest  circumference  of  the  animals  toward 


270  University  of  California  Publications  in  Zoology       [VoL- 20 

each  end,  which  is  comparable  with  the  arrangement  in  Stentor, 
though  in  the  latter  the  narrowing  must  necessarily  take  place  in  the 
posterior  direction  only.  The  above  author  mentions  the  branching 
of  stripes,  but  this  does  not  occur  in  Balanticfrium  so  far  as  I  have  been 
able  to  determine.  As  the  bands  pass  posteriorly,  however,  they 
become  less  distinctly  differentiated  and  are  hard  to  follow,  and  it 
might  be  that  further  study  with  more  intensive  stains  would  reveal 
a  union  in  the  region  of  convergence  at  the  posterior  end.  More  recent 
work  has  added  to  the  number  of  Heterotricha  that  show  this  sort  of 
differentiation  of  ectoplasm.  Maier  (1903)  shows  the  striped  nature 
of  this  layer  in  Prorodon  and  Spirostomum,  while  Neresheimer  (1903) 
confirms  the  structure  found  by  Johnson  ( 1893 )  in  Stentor.  Schuberg 
(1887)  also  indicates  a  comparable  plan  of  structure  in  Bursar  la. 
The  granular  ridges  of  ectoplasm  between  the  furrows  in  which  the 
anal  cirri  are  situated  in  Euplotes  patella,  discovered  by  Yocom 
(1918),  may  be  comparable  with  the  bands  which  occur  in  Hetero- 
tricha. 

Cilia. — The  entire  surface  of  Balanticbium  coli,  with  the  exception 
of  the  oral  plug,  is  thickly  beset  with  cilia  (cil.,  ador.  c.,  fig.  I).  These 
are  of  two  kinds,  viz.,  those  which  make  up  the  adoral  row  of  cilia 
and  which  measure  from  8  to  12/A  in  length,  and  those  covering  the 
body,  which  vary  from  4  to  6ju.  Those  covering  the  apical  cone  form 
an  intergradation  between  the  two.  On  this  surface  the  cilia  which 
occur  immediately  posterior  to  the  adoral  row  are  only  slightly  shorter- 
and  slightly  more  slender  than  the  adoral  cilia  themselves.  Passing 
posteriorly  they  gradually  become  shorter  and  less  cirrus-like  until 
they  reach  the  base  of  the  apical  cone.  Thence  posteriorly  they  retain 
the  uniform  size. 

The  body  cilia  are  comparatively  short  and  very  slender.  So  small 
are  they  in  fact  that  to  observe  a  single  one  is  nearly  impossible.  In 
slides  prepared  by  the  usual  methods  no  stain  remains  in  the  cilia  if 
destaining  is  carried  sufficiently  far  to  differentiate  other  structures. 
Iodine  (Weigert's  solution)  gives  a  fairly  satisfactory  stain  for  tem- 
porary mounts.  The  arrangement  of  cilia  may  be  determined  most 
readily  by  using  a  heavier  stain  and  then  observing  the  distribution 
of  basal  granules.  Neutral  red  proves  very  satisfactory  for  this  pur- 
pose. The  cilia  occur  in  longitudinal,  slightly  spiral  rows,  following 
the  grooves  between  the  ridges  in  the  pellicle.  These  rows  originate 
immediately  posterior  to  the  groove  in  which  the  adoral  cilia  are  set 
and  for  a  very  short  distance  pass  almost  meridionally ;  very  soon, 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      271 

however,  they  turn  toward  the  left,  that  is,  in  a  counter-clockwise 
direction  when  the  animal  is  viewed  from  a  point  exactly  in  front. 
They  continue  their  spiral  direction  until  almost  to  the  posterior  end 
when  they  again  follow  a  meridional  path  to  their  termination.  In 
passing  the  entire  length  of  the  body  any  single  row  of  cilia  twists  to 
the  left  approximately  120°,  or  one-third  the  entire  circumference. 
Whether  some  rows  terminate  or  become  continuous  with  contiguous 
rows  before  reaching  the  posterior  tip  of  the  animal,  I  have  been 
unable  to  determine,  for  both  basal  granules  and  granular  bands 
become  very  indistinct  in  this  region  even  in  the  best  preparations. 
The  number  of  rows  was  counted  with  difficulty  in  several  cross- 
sections  from  the  equatorial  regions  of  different  animals,  and  it  was 
found  to  vary  from  about  60  in  small  individuals  to  120  in  larger  ones. 
No  correlation  between  the  variation  in  the  number  of  rows  of  cilia 
and  the  species  of  the  animal  could  be  determined,  but  this  is  possibly 
due  to  the  limitation  of  observation. 

Basal  apparatus. — The  cilia  perforate  the  pellicle  and  attach  to 
the  basal  granules  which  lie  immediately  underneath  (fig.  L).  The 
latter  are  small  and  apparently  spherical  or  oval.  They  stain  very 
deeply  black  or  blue  with  haematoxylin.  In  the  living  animal  they 
are  readily  emphasized  by  the  use  of  neutral  red,  and  less  so  by  Janus 
green.  In  preparations  stained  with  Mallory's  connective  tissue  stain 
these  granules  show  brilliantly  red  with  the  acid  fuchsin,  as  do  the 
other  parts  of  the  neuromotor  apparatus  and  also  the  micronucleus. 
Longitudinally  the  granules  are  so  closely  placed  that  it  is  impossible 
to  observe  whether  they  are  actually  connected  by  a  fibre.  Cross- 
sections  show  that  the  cilia  of  one  row  have  no  transverse  connection 
by  any  sort  of  stainable  fiber  with  those  of  the  next  row.  The  rows 
of  basal  granules  lie  close  beneath  the  depression  in  the  pellicle  in 
the  hyaline  or  bright  band  of  the  ectoplasm.  A  ciliary  rootlet  (cil.  r., 
figs.  I  and  L)  extends  from  each  basal  granule  centrally  toward  the 
endoplasm.  It  does  not  proceed  in  an  exact  radial  line  but  rather 
diagonally  toward  the  right  until  it  enters  the  granular  band  near 
the  inner  surface  of  the  latter.  The  ciliary  rootlets  in  some  cross- 
sections  appear  to  have  an  exactly  radial  direction.  In  such  cases, 
however,  the  granular  band  is  somewhat  diagonal  in  the  opposite 
direction.  This  variation  is  probably  produced  either  by  torsion  of 
the  animal  or  by  the  direction  of  the  effective  beat  of  the  cilia  at  the 
instant  of  fixation.  The  diagonal  direction  of  the  rootlets  is  readily 
detected  in  tangential  sections.  In  focusing  down  through  such  a  sec- 


272  University  of  California  Publications  in  Zoology       [VOL.  20 

tion,  the  rootlet  is  invariably  seen  to  run  from  the  basal  granule 
toward  the  observer's  right  into  the  contiguous  granular  band  on  that 
side.  Thus,  to  avoid  any  confusion  that  might  arise  from  the  terms 
right  and  left,  in  a  cross-section  of  the  animal  viewed  from  the  anterior 
surface  (such  a  view  is  shown  in  fig.  L)  the  ciliary  rootlets  swerve  in 
the  counter-clockwise  direction  and  enter  the  granular  band  lying 
immediately  in  that  direction. 

As  the  rootlet  enters  into  the  granular  band  it  apparently  enlarges 
thus  forming  a  secondary  basal  granule.  In  some  cases  this  may  stain 
even  more  deeply  than  the  basal  granule  itself,  and  appear  as  a  definite 
body  somewhat  elongated  in  the  direction  of  the  circumference  of  the 
animal.  It  was  thought  at  first  that  this  might  be  the  cross-section  of 
a  longitudinal  fiber  or  myoneme.  But  the  study  of  numerous  tan- 
gential sections  has  failed  to  show  the  presence  of  any  longitudinal 
fiber  within  the  granular  band.  The  stainability  varies  greatly  and 
in  preparations  which  have  stained  lightly  the  ciliary  rootlets  appear 
to  fray  out  and  merge  into  the  granular  band,  while  still  retaining 
deeper  color  than  the  rest.  Which  interpretation  is  correct  it  is 
difficult  to  say,  but  the  latter  seems  the  more  probable,  especially  in 
view  of  certain  relations  with  the  neuromotor  apparatus  which  will 
be  discussed  later. 

Putter  (1903)  reproduces  a  figure  from  Studnicka  (1899)  showing 
in  a  schematic  way  five  types  of  attachment  of  the  cilia  with  their 
basal  apparatus.  Of  these,  two,  at  least,  represent  cases  in  which  two 
basal  granules  or  a  diplosome  are  present.  Saguchi  (1917)  in  his 
studies  on  ciliated  cells  of  Metazoa  says  in  part  regarding  the  basal 
granules  of  certain  ciliated  cells  from  amphibian  larvae,  '  *  With  favor- 
able staining  the  basal  corpuscles  appear  as  diplosome  or  dumbbell 
shaped  granules.  One  of  these  is  situated  at  the  upper  the  other  at 
the  lower  border  of  the  cuticle."  In  Balantidium  coli  the  arrange- 
ment with  respect  to  protoplasmic  layers  is  quite  different,  though 
the  cilia  seem  to  follow  somewhat  the  same  plan  of  structure  even  to 
the  presence  of  rootlets. 

The  most  fruitful  comparison  may  be  made  with  the  .basal  appa- 
ratus of  cilia  in  Isotricha  prostoma  as  described  and  pictured  by 
Braune  (1913).  In  this  organism  he  describes  diplosomic  structure 
of  the  basal  apparatus,  in  which  the  basal  granule  lies  directly  beneath 
the  pellicle.  The  cilia,  however,  extend  beyond  the  basal  granule  into 
the  underlying  layer — the  *  *  Zwischenschicht "  of  Eberlein,  and  ter- 
minate in  the  "Grenzschicht"  with  a  second  granule,  which  upon 


1922 J       McDonald:  On  Balantidium  coli  and  Balantidium  suis      273 

maceration  remains  attached  to  the  basal  end  of  the  cilium.  So  the 
basal  apparatus  in  Balantidium  coli  even  to  the  relative  location  of 
the  basal  granules  is  almost  identical  with  that  in  Isotricha  prostoma. 
In  Balantidium,  however,  as  mentioned  above,  the  "Grenzschicht" 
seems  to  be  lacking.  The  comparison  becomes  more  significant  in  view 
of  the  fact  that  both  ciliates  are  parasitic  in  the  digestive  tract  of 
mammals,  and  both  are  in  much  the  same  state  with  reference  to 
the  degree  of  specialization  and  degeneration  correlated  with  habits 
of  the  parasitic  mode  of  life.  So  that  in  general  •  morphology  they 
seem  to  be  more  alike,  though  they  are  in  separate  orders,  than  do 
Diplodinium  ecaudatum  and  Balantidium  coli,  which  are  in  separate 
suborders  only. 

Ciliary  Movements. 

Locomotion  is  the  chief  function  of  the  cilia  except  for  those  of 
the  adoral  zone.  The  balantidia  swim  in  approximately  a  straight 
line  and  not  in  a  spiral  course  as  do  paramoecia.  They  do,  however, 
rotate  on  their  axis  as  they  progress.  This  rotation  is  generally  from 
left  to  right,  that  is,  in  a  counter-clockwise  direction  when  viewed  from 
a  point  in  front  of  the  animal.  A  few  instances  of  reversal  of  the 
direction  have  been  seen,  but  it  is  not  at  all  common.  The  direction 
of  rotation,  i.e.,  from  left  to  right,  seemed  at  first  inexplicable,  since 
this  was  not  compatible  with  the  direction  of  the  rows  of  cilia.  The 
rows  of  cilia,  as  described  above,  are  comparable  to  the  threads  of  a 
left-hand  screw.  In  order  to  penetrate,  such  a  screw  must  be  turned 
in  a  clockwise  direction  (when  viewed  from  the  point,  not  from  the 
head).  Such,  also,  is  the  direction  of  rotation,  of  balantidia  which  one 
would  expect  to  find  if  the  arrangement  of  the  cilia  were  the  con- 
trolling factor,  but  the  rotation  is  in  the  reverse  direction.  In  the 
further  study  of  the  problem,  I  fortunately  obtained  some  very  thin 
tangential  sections  of  animals  on  which  the  fixative  had  acted  so 
quickly  that  the  cilia  were  stopped  instantly  and  left  in  the  relative 
positions  assumed  in  normal  ciliary  action. 

Figure  N  is  a  camera  lucida  drawing  of  such  a  section.  By  analysis 
of  the  position  of  the  cilia  on  this  and  other  like  sections,  it  was 
possible  to  determine  the  complete  cycle  of  a  single  cilium.  This  cycle 
is  diagrammatically  represented  in  figures  M  and  0.  Figure  N 
includes  about  two  and  one-half  cj^cles  of  action  as  represented  by 
the  waves.  The  dark  portions  are  produced  by  the  prostrate  position 
of  the  cilia  at  the  termination  of  the  effective  stroke.  The  lighter 


274  University  of  California  Publications  in  Zoology       tv°L- 20 


areas  between  are  due  to  the  fact  that  the  cilia  are  recovering  their 
vertical  position  and  hence  are  viewed  very  nearly  endwise.  The 
position  of  consecutive  cilia  in  any  single  row,  from  one  point  in  a 
wave  to  a  similar  point  in  a  following  wave  will  fairly  represent  the 
successive  positions  taken  by  a  single  cilium  in  making  one  complete 
cycle.  Figure  M  was  made  in  this  way.  The  arrow  represents  the 
long  axis  of  the  animal.  From  this  diagram  it  is  seen  that  the  cilium 
at  the  end  of  the  effective  stroke  lies  rather  close  to  the  surface  of 
the  body  and  not  along  the  row  but  decidedly  to  the  left  from  it.  In 


-a 


Fig.  M 


Fig.  N 


Fig.  O 


Fig.  M.  Diagrammatic  representation  of  the  successive  steps  in  one  complete 
beat  of  a  cilium  of  Balantidium  coli.  It  also  illustrates  the  positions  of  the  respec- 
tive cilia  of  a  single  row  between  the  points  a  and  &  in  fig.  M,  at  which  points  the 
cilia  are  in  a  prostrate  position  at  the  end  of  their  effective  stroke.  The  arrow 
indicates  the  long  axis  of  the  animal. 

Fig.  N.  Tangential  section  of  Balantidium  coli.  The  cilia  still  retain  respec- 
tive positions  which  they  had  in  the  normal  swimming  movements  of  the  organism. 
X  1500. 

Fig.  O.  Diagram  illustrating  the  effect  of  the  ciliary  action  in  the  rotation  of 
the  organism.  The  arrow  represents  the  long  axis  of  the  animal;  ab.,  the  direction 
of  the  rows  of  cilia ;  cd.,  the  direction  of  effective  stroke  of  a  cilium  attached 
at  the  point  of  intersection  of  the  three  lines;  the  ellipse  is  described  by  the  tip 
of  the  cilium. 

recovery  it  straightens  up  and  passes  anteriorly,  thence  to  the  right, 
crossing  the  row,  of  which  it  is  a  part,  at  right  angles.  At  this  point 
the  cilium  leans  anteriorly  only  slightly  from  the  vertical.  The 
effective  beat  is  produced  by  the  quick  stroke  of  the  cilium  posteriorly 
and  to  the  left,  and  continues  until  the  cilium  has  crossed  the  row  again 
and  lies  close  to  the  surface  and  extends  to  the  left  as  represented 
by  the  position  of  the  last  cilium  shown  in  figure  M.  According  to 
the  classification  given  by  Putter  (1903),  the  movement  of  the  cilia 
of  Balantidium  would  be  called^  infundibular.  As  will  be  noted  from 


1922]      McDonald:  On  Balantidium  eoli  <md  Balantidium  suis      275 

figure  0,  the  funnel  described  by  the  complete  beat  .of  the  cilium 
is  somewhat  irregular,  the  rim  outlined  by  the  tip  of  the  cilium  is 
elliptical,  and  the  base  of  the  cilium,  i.e.,  the  neck  of  the  funnel,  is 
not  central  but  is  situated  below  the  anterior  focus  of  the  ellipse. 
The  ellipse  described  by  the  tip  of  the  cilium  lies  in  a  plane  which  is 
not  parallel  to  the  surface  of  the  animal,  but  which  approaches  it 
much  more  closely  posteriorly.  It  was  possible  to  corroborate  the 
action  of  the  cilia  in  observations  on  the  living  material.  The  cilia  of 
the  apical  cone  are  somewhat  larger  than  the  other  cilia  of  the  body, 
and  are  closely  coordinated  in  their  action.  In  balantidia  which  were 
allowed  to  cool  until  action  had  slackened  considerably,  these  cilia 
were  observed  to  make  their  effective  stroke  at  a  decided  angle  to  the 
rows  of  cilia.  For  instance,  in  the  boring  action  in  connection  with 
the  process  of  penetration  described  above,  these  cilia  will  beat  in  an 
almost  exactly  transverse  direction,  always  from  right  to  left.  In 
further  corroboration  of  this  interpretation  of  the  movements  of  the 
cilia  is  the  fact  that  it  explains  the  rotation  of  the  animal  during 
progression.  It  will  be  seen  from  figure  0  that  the  effective  stroke 
of  any  single  cilium  will  be  in  the  direction  cd.  This  line  crosses  both 
the  arrow,  representing  the  long  axis  of  the  animal,  and  the  line  a&, 
representing  the  rows  of  cilia,  making  an  angle  of  approximately 
20°  with  the  latter.  That  is,  the  line  cd  forms  an  angle  with  the  arrow 
on  one  side  about  equal  to  the  angle  on  the  opposite  side  made  by  the 
line  ah.  It  clearly  follows  that  if  the  effective  stroke  is  in  the  direction 
cd  then  rotation  will  be  from  left  to  right  and  not  vice  versa  as  would 
be  the  case  if  the  cilia  beat  in  the  direction  of  the  rows  in  which  they 
are  arranged.  The  structure  of  the  basal  apparatus  is  significant  in 
view  of  the  direction  of  the  effective  stroke  of  the  cilia,  viz.,  posteriorly 
and  to  the  left.  The  cross-section  shown  in  figure  L  is  viewed  anter- 
iorly and  shows  that  the  ciliary  rootlet  from  each  basal  granule  passes 
to  the  right  and  enters  the  granular  band  on  that  side  of  the  hyaline 
band  in  which  the  basal  granule  lies.  Without  giving  to  the  ciliary 
rootlets  any  motor  or  skeletal  function,  it  still  seems  logical  that  they 
conform  in  a  general  way  to  the  axis  of  the  cilium,  for  the  latter  during 
the  greater  part  of  its  movement  inclines  to  the  posterior  and  left  of 
the  row  of  which  it  is  a  constituent. 

The  peristome  (per.  fig.  J)  may  be  said  to  comprise  all  that  part 
of  the  organism  which  lies  within  the  row  of  adoral  cilia.  In  the 
active  animal  it  is  variable  in  shape.  At  times  it  is  almost  round 
while  at  other  times  it  may  become  a  mere  slit  or  groove.  In  what 


276  University  of  California  Publications  in  Zoology       [V°L-  20 

seems  to  be  its  more  normal  proportions,  however,  it  is  approximately 
pear-shaped  with  the  stem  end  of  the  pear  directed  ventrally.  In 
Balantidium  eoli  the  adoral  zone  commonly  includes  the  most  anterior 
point  or  apex  of  the  animal — at  least  its  dorsal  margin  passes  through 
this  point.  In  Balantidium  suis,  the  anterior  tip  of  the  animal  lies 
wholly  outside  of  this  zone,  the  latter  having  migrated  too  far  ventrally 
to  include  it. 

The  cytostome  (cytst.,  fig.  J)  does  not  occupy  the  whole  interior 
of  the  peristome,  but  is  situated  at  its  ventral  end.  There  is  some 
indication  that  this  aperture  may  be  completely  closed  by  the  oral 
plug  (or.  pi.,  fig.  I)  which  comprises  the  rest  of  the  peristome  within 
the  adoral  row  of  cilia.  This  oral  plug  bears  no  cilia.  It  is  exceed- 
ingly mobile,  adapting  itself  readily  to  the  almost  constantly  changing 
shape  of  the  apical  cone.  It  lies  dorsal  to  the  cytostome  and  is  not 
exactly  bilaterally  symmetrical  since  it  is  pushed  somewhat  to  the  left 
to  make  room  for  the  oesophagus.  It  extends  inward,  thinning  as 
it  does  so,  until  it  terminates  about  the  beginning  of  the  endoplasm. 
It  is  ectoplasmic,  but  very  finely  granular  as  compared  with  the  rest 
of  the  ectoplasm.  Mallory's  connective  tissue  stain  ordinarily  gives 
it  a  decidedly  bluish  tinge  with  slight  spots  of  red  only  where  there 
are  certain  neuromotor  fibers.  Its  action  in  feeding  is  very  hard  to 
follow,  but  its  high  degree  .of  mobility  impresses  one  when  watching 
the  activities  of  the  organism,  and  may  be  demonstrated  with  fixed 
material  by  its  extreme  protrusion  (pi.  28,  fig.  14).  In  addition  to 
this,  the  fact  that  it  is  intimately  connected  with  the  neuromotor 
apparatus  would  indicate  that  it  functions  in  selective  feeding.  The 
oesophagus  (oes.,  fig.  I;  pi.  27,  figs.  4—8)  beginning  at  the  cytostome, 
passes  inwardly,  not  quite  radially  but  swerving  slightly  to  the  right. 
It  may  be  followed  definitely  through  the  ectoplasm  and  for  a  very 
short  way  into  the  endoplasm  where  it  ends  blindly.  So  far  as  I 
have  been  able  to  determine,  it  is  a  uniform  tube-like  opening  without 
evident  enlargements  or  constrictions.  Prowazek  (1913),  however, 
gives  in  part  the  following  description,  ".  .  .  .  es  sehnt  sich  jedoch 
nicht  direct  trichterformig  in  die  Tiefe,  da  man  von  der  drei  scharfe 
Konturen  noch  nachweisen  kann  (fig.  1)."  While  studying  living 
forms  stained  with  neutral  red,  I  have  often  observed  specimens  in 
the  exact  position  of  the  one  shown  by  Prowazek  (1913,  p.  7,  text 
fig.  1).  The  lines  shown  by  him  were  easily  recognizable,  deeply 
stained  with  the  neutral  red,  but  I  could  interpret  them  only  in  the 
following  way.  The  most  anterior  line  which  he  shows  seems  to  be 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      277 

clearly  the  ventral  lip  of  the  peristome ;  the  second  line  was  identical 
with  the  deep  staining  motorium  (fig.  I)  in  the  forms  which  I  studied, 
and  the  most  posterior  line  seemed  identical  with  the  ring  of  enlarge- 
ments on  the  rootlets  of  the  adoral  cilia  which  lie  close  about  the 
oesophagus.  The  margin  of  the  peristome  is  slightly  raised^  forming 
a  ridge  or  lip.  This  ridge  is  most  pronounced  from  the  midventral 
point,  dorsal  along  the  right  margin  of  the  cytostome,  but  as  it  pro- 
ceeds around  it  becomes  rather  inconspicuous  and  wholly  disappears 
on  the  left  side.  Thus  the  cytostome  has  the  appearance  of  opening 
under  a  ledge,  the  ledge  formed  by  the  lip  of  the  right  side. 

The  peristome  is  delimited  by  an  almost  complete  spiral  circlet  of 
cilia,  the  adoral  cilia  (ad.  cil.,  fig.  I).  The  exact  point  of  origin  of 
the  row  is  hard  to  determine  but  it  is  approximately  at  the  ventral 
edge  of  the  peristome,  i.e.,  on  the  ventral  lip  of  the  cytostome.  From 
here  it  proceeds  in  a  sort  of  groove,  along  the  right  margin,  around 
the  dorsal  margin,  and  down  the  left  margin  of  the  peristome.  A 
short  distance  in  advance  of  the  ventral  point,  the  row  of  adoral  cilia 
turns  into  the  cytostome  and  continues  in  a  spiral  course  down  the 
oesophagus ;  entering  at  the  left  dorsal  side  and  ending  in  the  ventral 
wall  about  halfway  down.  Thus  these  cilia  in  their  entire  course  make 
one  complete  left-hand  spiral,  beginning  on  the  ventral  lip,  passing 
around  the  peristome  and  down  the  oesophagus,  terminating  in  its 
ventral  wall. 

Over  the  lip  of  the  cytostome  between  the  point  where  the  adoral 
cilia  turn  into  the  oesophagus  and  the  midventral  point  where  this 
row  of  cilia  has  its  origin,  the  longitudinal  rows  of  body  cilia  turn  in. 
Each  of  these  rows,  of  which  there  are  ten  or  twelve  altogether,  con- 
tinues down  the  oesophagus  until  it  meets  the  row  of  adoral  cilia. 
Since  this  latter  enters  spirally,  there  is  a  ciliated  patch  on  the  ventral 
wall  of  the  funnel-shaped  'oesophagus  which  is  roughly  the  shape  of  a 
right  triangle,  the  base  of  which  is  the  lip  of  the  cytostome.  The 
hypotenuse  is  the  row  of  adoral  cilia  which  makes  an  acute  angle  with 
the  longitudinal  row  of  body  cilia  which  enters  in  the  mid  line  and 
which  represents  the  third  side  of  the  triangle. 

The  adoral  cilia,  except  where  they  lie  within  the  oesophagus,  are 
completely  separate  each  from  the  other.  This  is  easily  verified  by 
watching  their  action  especially  in  a  disintegrating  animal,  or  one 
cooled  to  slow  up  ciliary  movement,  under  which  condition  coordina- 
tion is  frequently  interrupted,  and  a  single  cilium  will  be  seen  acting 
independently  of  its  neighbor.  Additional  evidence  is  to  be  found  in 


278  University  of  California*  Publications  in  Zoology       [VOL.  20 

the  individuality  of  each  basal  granule.  There  is  no  evidence  of  fusion 
of  granules,  though  adjoining  granules  are  connected  by  a  neuromotor 
fiber.  However,  in  the  triangular  area  mentioned  above,  there  is  con- 
siderable evidence  that  the  cilia  are  united  to  form  membranelles.  It 
is  very  difficult  to  watch  the  action  of  these  cilia,  and  the  above  con- 
clusion was  reached  largely  through  a  study  of  fixed  material.  In 
cross-sections  (pi.  27,  fig.  4)  the  cilia  of  the  region  seem  to  be  very 
close  together  and  quite  regularly  to  be  connected  by,  or  to  form,  a 
sheet  of  almost  transparent  substance.  The  regularity  of  this  occur- 
rence would  lead  one  to  believe  that  it  is  the  normal  structure  and  not 
due  to  entanglement  of  the  cilia  in  foreign  matter.  In  addition,  the 
basal  granules  of  this  region  (pi.  27,  figs.  4  and  5)  do  not  stand  out 
separately,  but  are  so  closely  packed  that  they  give  the  appearance 
of  a  single  deeply  stained  mass.  I  have  been  unable  to  distinguish 
separate  granules  in  the  inner  portion  of  the  area  and  it  seems  likely 
that  actual  fusion  of  the  granules  may  have  occurred.  The  basal 
apparatus  of  this  region  is  so  densely  packed  and  takes  stain  so  readily 
that  in  certain  views  it  may  easily  be  mistaken  for  the  motorium.  As 
a  result,  it  seems  plausible  to  interpret  this  area  as  the  basal  apparatus 
of  membranelles  which  lie  in  a  plane  transverse  to  the  axis  of  the 
oesophagus.  If  this  region  be  interpreted  as  a  primitive  oral  groove 
or  cytostome,  a  forerunner  of  such  an  elaborate  arrangement  as  occurs 
in  Euplotes  patella  (Yocum,  1918)  or  in  Stentor,  then  comparison  is 
very  significant,  for  in  the  latter  two  the  membranelles  also  run  trans- 
versely in  the  cytostome.  The  only  difference,  then,  between  these 
organisms  and  Balantidium  in  this  regard  would  be  the  difference  in 
shape  and  extent  of  the  area. 

The  adoral  cilia  (ad.  til.,  fig.  I)  are  approximately  double  the 
length  of  the  body  cilia,  i.e.,  from  6/x  to  S/A  in  length  or,  in  the  very 
large  individuals,  they  may  reach  a  maximum  length  of  10/x.  In 
fundamental  structure  they  are  like  the  body  cilia,  but  the  relative 
position  of  parts  is  somewhat  different.  Immediately  beneath  the 
pellicle  each  cilium  bears  a  basal  granule  and  from  this  a  fiber  con- 
tinues inward  which  passes  between  the  adoral  plug  and  the  surround- 
ing ectoplasm.  The  sum  of  all  the  fibers  from  adoral  cilia  marks  off 
very  distinctly  the  conical  cytostomal  region  from  the  surrounding 
ectoplasm.  They  seem  to  constitute  the  only  partition  between  the 
protoplasm  of  the  two  areas,  for  I  have  not  been  able  to  detect  any 
membrane  in  this  region  making  a  complete  separation  of  the  adoral 
region  from  the  rest  of  the  apical  cone.  Where  the  fibers  pass  from 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      279 

the  ectoplasm  of  this  cone  into  the  endoplasm,  each  bears  an  enlarge- 
ment which  stains  very  deeply.  This  enlargement  is  undoubtedly 
homologous  with  the  inner  enlargements  of  the  basal  apparatus  of 
the  body  cilia  for  it  bears  the  same  relation  to  the  basal  granule  and 
the  cilium.  It  is  farther  removed  from  the  basal  granule  but  it  main- 
tains exactly  the  same  relation  to  the  ectoplasm  and  endoplasm,  that 
is  to  say,  in  either  case  this  enlargement  lies  in  the  plane  between  the 
two.  From  each  enlargement  a  radial  fiber  extends  laterally  along 
the  base  of  the  apical  cone  to  the  periphery  of  the  cell.  The  portion 
of  the  ciliary  rootlet  which  continues  inward  from  this  enlargement  is 
very  distinct  and  may  often  be  traced  almost  to  the  posterior  end  of 
the  animal  (fig.  I).  In  no  instance  has  it  been  possible  to  demonstrate 
any  attachment  or  connection  of  the  posterior  ends  of  these  rootlets. 
They  often  cross  near  the  center  of  the  organism  and  then  fade  out, 
becoming  indistinguishable  in  the  endoplasm.  For  a  short  distance 
inward  from  the  oesophagus  they  are  so  closely  placed  dorsally  and 
laterally  that  they  form  a  kind  of  wall,  but  ventrally  they  are  less 
numerous  and  likely  to  be  much  shorter,  so  that  the  pseudo-wall  is 
not  complete.  It  is  sufficient,  however,  to  direct  the  food  for  some 
distance  into  the  endoplasm.  There  is  no  such  high  degree  of  differ- 
entiation here  as  Sharp  (1914)  found  in  the  oesophagus  of  Diplo- 
dinium  ecaudatum. 

The  homology  of  the  adoral  and  body  cilia  is  evidenced  by  the  com- 
plete series  of  gradations  from  the  one  to  the  other  which  exist  in  the 
cilia  of  the  apical  cone  (fig.  I).  The  cilia  which  are  proximal  to  the 
adoral  cilia  are  almost  identical  with  them.  They  are  slightly  smaller, 
but  each  has  the  basal  granule  beneath  the  pellicle,  a  fiber  connecting 
this  with  an  enlargement  at  the  plane  of  differentiation  of  ectoplasm 
from  endoplasm,  and  the  rootlet  extending  posteriorly.-  The  inner  en- 
largement is  much  smaller  and  the  ciliary  rootlet  shorter  than  those  of 
the  adoral  cilia.  These  enlargements  are  connected  with  the  enlarge- 
ments of  the  adoral  cilia  by  the  radial  fibers  mentioned  above.  Passing 
posteriorly  the  cilia  become  progressively  smaller,  the  basal  granule 
and  the  enlargement  closer  together  (due  to  the  approach  of  the  trans- 
verse plane  of  demarcation  between  ectoplasm  and  endoplasm  to  the 
pellicle),  and  the  ciliary  rootlets  become  progressively  shorter  and  less 
distinct,  until  the  cilia  of  the  marginal  area  of  the  apical  cone  become 
identical  with  the  body  cilia.  This  apical  cone  then  shows  us  a  com- 
plete gradation  of  differentiation  between  the  body  cilia  and  the  adoral 
cilia,  and  proves  their  homology. 


280  Umverstiy  of  California  Publications  in  Zoology       [VOL.  20 

Feeding  is  the  chief  function  of  the  adoral  cilia.  They  are  closely 
coordinated  in  action,  as  is  shown  by  the  fact  that  in  degenerating  in- 
dividuals they  will  beat  in  unison  after  other  cilia  beat  only  erratically 
or  have  ceased  entirely.  Coordination  is  most  pronounced  in  the  cilia 
of  the  left  lip.  The  action  of  the  adoral  cilia  produces  a  strong  eddy 
in  the  surrounding  medium  with  the  vortex  of  the  eddy  within  the 
peristome.  In  the  above  description  it  was  noted  that  the  right  lip 
projected  slightly  forming  a  ledge  or  bank.  The  current  produced 
by  the  cilia  strikes  against  this  ledge  and  solid  objects  are  deflected 
into  the  underlying  cytostome.  The  natural  rotation  of  the  animal 
on  its  longitudinal  axis  as  described  above  aids  in  this  process,  for  the 
right  lip  thus  acts  as  the  blade  of  an  auger.  The  food  particles  pass 
down  the  oesophagus  and  collect  at  the  inner  end  in  a  sort  of  droplet. 
After  several  bits  have  been  collected,  the  droplet  begins  its  circulation 
in  the  endoplasm  as  a  food  vacuole. 

The  closure  of  the  cytostome  in  all  probability  is  effected  by  the 
oral  plug.  The  latter  is  very  mobile  and  contains  fibers  of  the  neuro- 
motor  apparatus.  It  has  frequently  been  seen  to  project  anteriorly 
in  a  knoblike  protrusion  (pi.  28,  fig.  14).  This  same  phenomenon  was 
observed  by  Wising  (1871).  In  view  of  its  situation,  its  sensitivity, 
and  its  mobility,  it  seems  plausible  to  interpret  it  as  an  oral  plug 
with  essentially  the  same  function  as  the  oral  disk  of  Diplodinium 
ecaudatum  (Sharp,  1914). 

The  discharge  of  indigestible  portions  of  the  food  takes  place  at 
a  constant  point  at  the  posterior  end  of  the  animal,  the  cytopyge  (cyt., 
fig,  I).  It  is  an  opening,  however,  only  at  the  time  of  discharge. 
At  other  times  there  is  only  a  thinning  of  the  cortical  layer  which  can 
be  identified  with  comparative  ease  in  fixed  material.  In  the  living 
organism  the  process  of  defecation  was  frequently  observed.  The 
undigested  particles  become  segregated  at  the  extreme  posterior  end 
in  a  sort  of  vacuole,  the  rectal  vacuole  (ret.  v.,  fig.  I;  pi.  28,  fig.  13). 
After  this  vacuole  has  become  of  considerable  size  (often  filling  one- 
third  of  the  cell  in  degenerating  forms)  the  pellicle  over  the  cytopyge 
ruptures  and  the  contents  are  discharged.  The  pellicle  quickly  forms 
again  closing  the  aperture,  collection  of  indigestible  particles  in  the 
rectal  vacuole  continues,  and  the  process  is  repeated. 

The  contractile  vacuoles  (post.  c.  v.,  ant.  c.  v.,  fig.  I)  are  two  in 
number,  usually  situated  on  the  dorsal  side,  one  anteriorly,  well  up 
toward  the  apical  cone,  the  other  in  the  posterior  one-third  of  the 
organism.  There  is  a  great  deal  of  variation  in  their  location  in 
different  animals,  though  in  the  individual  their  situation  seems  to  be 


1922]       McDonald:  On  Ealantidium  coli  and  Balantidium  suis      281 

very  constant,  at  least  throughout  the  limit  of  possible  observation. 
These  vacuoles  seem  clearly  to  originate  within  the  ectoplasm.  When 
fully  distended  they  encroach  far  upon  the  region  of  the  endoplasm 
and  it  becomes  impossible  to  tell  whether  or  not  they  are  entirely  sur- 
rounded by  ectoplasm ;  but  from  their  origin  such  might  be  suspected 
to  be  the  case.  Also  such  is  the  case  in  many  related  forms,  for 
example,  Diplodinium  eodudatum  (Sharp,  1914)  and  Euplotes  patella 
(Yocom,  1918). 

The  pulsation  of  the  vacuoles  was  observed  in  several  instances 
for  a  long  period  of  time.  The  rate  of  pulsation  varies  considerably, 
occurring  as  rapidly  as  once  in  every  thirty  seconds  under  some 
conditions,  while  under  others  a  complete  cycle  from  discharge  to 
discharge  occupies  a  period  of  five  minutes.  In  degeneration  the 
pulsation  is  likely  to  be  very  much  retarded  or  may  cease  entirely, 
the  vacuoles  becoming  enormously  distended  and  breaking  together 
thus  forming  one  large  vacuole  occupying  fully  one-half  of  the  interior 
of  the  organism.  Following  this  the  animal  ruptures  and  disintegrates. 
The  observation  of  a  considerable  number  of  normal  individuals  has 
shown  the  usual  cycle  to  be  as  follows.  At  two  points  in  the  ectoplasm 
small  droplets  of  clear  liquid  appear.  These  increase  in  size  and 
become  the  vacuoles  usually  seen.  Contributing  vacuoles  or  channels 
such  as  occur  in  Paramaecium  have  never  been  noted.  When  they  have 
reached  sufficient  size  (10/x,  to  15/*  in  diameter  in  the  ordinary  indi- 
vidual), they  change  from  their  spherical  shape  and  begin  to  bulge, 
each  on  the  side  toward  the  other.  These  bulges  elongate  until  they 
meet  at  a  midpoint.  At  this  midpoint  a  new  vacuole  arises  and  into 
it,  through  the  channels  thus  formed,  the  two  vacuoles  discharge  their 
contents.  This  large  middle  vacuole  almost  immediately  discharges 
to  the  exterior  through  the  pellicle,  and  at  the  same  time  the  other 
two  vacuoles  re-form.  However,  the  discharge  of  the  middle  vacuole 
may  be  delayed  until  the  other  two  are  well  formed  and  then  the 
individual  has  three  vacuoles  present.  This  and  other  variations  are 
not  uncommon  and  should  be  taken  into  account  in  the  use  of  the 
number  of  vacuoles  as  a  basis  for  classification.  Leuckart  (1861) 
described  a  third  contractile  vacuole  though  he  did  not  give  its  rela- 
tive position  to  the  other  two  and  he  did  not  describe  the  process  of 
contraction.  He  reported  that  he  had  observed  the  vacuoles  "drop- 
like"  through  the  cytoplasm  and  wandering  from  place  to  place. 
Solojew  (1901)  described  the  two  vacuoles  and  observed  a  canal  con- 
necting the  two,  but  he  did  not  explain  its  function  in  discharge  of 
the  contents. 


282  University  of  California  Publication*  in  Zoology       [VOL.  20 


ENDOPLASMIC  STRUCTURES 

Endoplasm. — Within  the  ectoplasm  the  body  is  composed  of  the 
endoplasm  (end.,  pi.  27,  figs.  7  and  8;  pi.  28,  figs.  9  to  12)  and  the 
inclusions  therein.  The  endoplasm  is  less  dense  than  the  ectoplasm 
and  more  coarsely  granular.  It  is  quite  fluid,  having  a  fairly  definite 
circulation  in  the  active  organism.  From  the  inner  end  of  the 
oesophagus  the  direction  of  flow  is  posteriorly  along  the  ventral  sur- 
face dorsalward  just  before  reaching  the  posterior  end,  thence  an- 
teriorly along  the  dorsal  surface.  Just  as  it  reaches  the  ectoplasm 
of  the  apical  cone,  it  is  deflected  posteriorly  down  through  the  central 
portion  of  the  body  dorsal  to  the  rootlets  of  the  adoral  cilia.  This 
course  can  be  followed  readily  by  observing  the  circulation  of  the  food 
vacuoles. 

The  food  vacuoles  are  customarily  globular  and  may  contain  starch 
granules,  bacteria,  or  indigestible  particles,  of  the  food  of  the  host. 
The  ingestion  of  bacteria  is  probably  abnormal  since  it  seldom  occurs 
except  when  the  number  of  bacteria  in  the  medium  has  increased 
greatly  during  incubation.  The  starch  granules  may  occur  in  enor- 
mous numbers  especially  when  the  host  has  recently  been  fed  on  grain. 
Red  blood  cells  have  not  been  noted  in  any  of  the  balantidia  observed 
during  the  work. 

That  Balantidium  may  be  cannibalistic  is  the  only  possible  in- 
terpretation of  several  findings.  In  these  instances  small  individuals 
were  lying  within  the  endoplasm  of  extremely  large  individuals 
(100  X  125/i)  and  were  in  a  state  of  disintegration.  The  larger  indi- 
viduals were  Balantidium  coli  in  every  case  and  the  smaller  may  have 
been  Balantidium  suis,  for  both  species  were  present  in  the  material ; 
but  disintegration  of  the  latter  had  progressed  so  far  that  specific 
identification  was  uncertain.  The  possibility  of  interpreting  this 
phenomena  as  sporulation,  which  was  described  by  Walker  (1909), 
is  precluded  by  the  disintegration  of  the  included  organism  and  the 
fact  that  the  normal  vegetative  phase  of  the  nuclei  of  the  large  indi- 
vidual is  unmodified.  Further  evidence  is  to  be  found  in  the  fact 
that  never  more  than  a  single  individual  has  been  found  inside 
another,  while  sporulation  would  produce  several. 

Macronucleus. — As  is  generally  the  case  in  ciliates,  balantidia  are 
binucleate,  having  a  large  macronucleus  and  a  small  micronucleus. 
The  macronuclei  of  Balantidium  coli  and  Balantidium  suis  are  slightly 


1922]      McDonald:  On  Balantidium  eoli  and  Balantidium  suis      283 

different  with  respect  to  size  and  proportions  as  noted  above  (page 
259),  but  structurally  they  are  so  closely  alike  that  one  description 
will  suffice  for  both.  The  macronucleus  (mac.,  fig.  I,  pi.  28,  figs.  13 
and  14)  always  lies  in  the  endoplasm  but  otherwise  is  not^constant 
in  location.  Immediately  surrounding  it  is  an  area  in  which  the  endo- 
plasm is  less  granular  and  less  dense  in  appearance,  due  perhaps  as 
Yocom  (1918)  has  suggested  of  Euplotes  patella  to  more  rapid  oxida- 
tion in  this  region.  It  is  elongate  and  may  be  straight  and  rodlike 
or  it  may  be  sharply  bent  into  a  horseshoe  shape.  In  any  case  its 
diameter  increases  toward  either  end,  giving  it  something  of  a  dumb- 
bell shape.  This  constriction  in  the  central  region  and  enlargement 
at  each  end  is  more  marked  in  Balantidium  coli  than  in  Balantidium 
suis.  The  nucleus  is  delimited  by  a  definite  nuclear  membrane 
(nuc.  m.,  fig.  I)  which  is  especially  apparent  in  material  in  which 
the  macronucleus  has  shrunk  due  to  faulty  technique.  Within  this 
membrane  are  packed  rather  densely  the  masses  of  chromatin.  The 
chromatin  never  occurs  in  equal  sized  regular  granules  but  rather  in 
unequal  very  irregular  masses,  sometimes  of  considerable  size  (1  to  2/x, 
in  greatest  dimension).  Often  there  is  a  sort  of  vacuolated  area, 
usually  near  one  end  of  the  macronucleus,  which  is  free  from  chroma- 
tin.  The  significance  of  this  vacuolated  area  I  could  not  determine. 
It  does  not  seem  to  be  due  to  degeneration  and  is  not  related  to  any 
phase  of  reproduction.  It  is  in  no  way  comparable  to  the  ' '  reconstruc- 
tion band"  described  by  Griffin  (1910)  and  by  Yocom  (1918)  in 
Euplotes  worcesteri  and  Euplotes  patella,  respectively.  The  chromatin 
stains  black  with  haematoxylin  so  that  the  macronucleus  is  the  most 
conspicuous  structure  in  a  stained  individual.  When  Mallory's  con- 
nective tissue  stain  is  used,  the  macronucleus  takes  on  an  orange  hue. 
Micronucleus. — The  micronuclei  (mic.,  fig.  I)  of  both  species  of 
Balantidium  parasitic  in  pigs  are  exceedingly  small,  not  exceeding 
5/x.  in  diameter.  In  the  resting  or  vegetative  phase  the  micronucleus 
is  subspherical  and  its  flattened  side  lies  close  against  the  nuclear 
membrane  of  the  macronucleus.  It  may  even  lie  in  a  depression  in 
the  macronucleus  in  which  position  it  is  scarcely  distinguishable  from 
the  granules  of  the  latter.  It  is  surrounded  by  a  nuclear  membrane 
readily  recognized  when  the  micronucleus  is  undergoing  mitosis.  In 
a  few  instances  the  chromatin  has  appeared  indistinctly  granular  but 
it  is  customarily  so  closely  packed  that  it  looks  like  a  single  solid  mass. 


284  University  of  California  Publications  in  Zoology       [V°L.  20 


NEUROMOTOR  APPARATUS 

The  term  neuromotor  apparatus  denotes  an  integrated  system  of 
fibers,  with  a  coordinating  center,  which  is  present  in  some  Protozoa, 
and  which  is  credited  with  the  power  of  conductivity  of  nervous  im- 
pulses, and  hence  functions  in  the  coordination  of  the  motor  organelles 
of  the  cell.  The  term  was  first  used  for  ciliates  by  Sharp  (1914)  in 
his  account  of  the  structure  of  Diplodiniwm  ccaudatum.  Since  then 
it  has  been  employed  by  Kofoid  and  Christiansen  (1915),  Kofoid 
(1916)  for  flagellates,  and  by  Yocom  (1918)  and  by  Taylor  (1920) 
in  their  studies  of  the  morphology  and  behavior  of  Euplotes  patella. 

The  neuromotor  apparatus  of  Balantidium  coli  can  scarcely  be 
considered  apart  from  the  motor  organelles  of  the  cell.  To  insure 
clarity  in  the  description  and  discussion  which  follows,  the  motor 
organelles,  previously  described  in  some  detail,  will  be  briefly  reviewed. 
With  the  exception  of  the  oral  plug  which  surrounds  the  cytostome 
the  organism  is  thickly  beset  with  cilia.  Of  these,  the  adoral  cilia  are 
largest.  They  are  distributed  about  the  margin  of  the  peristome  in 
a  row  which  ends  in  the  membranellar  region  in  the  ventral  wall  of 
the  oesophagus.  The  rootlets  of  these  cilia  are  exceedingly  long,  reach- 
ing well  into  the  posterior  third  of  the  cell,  where  they  end  without 
any  connection  or  attachment.  They  have  two  enlargements,  the  first 
being  the  basal  granule  which  lies  just  beneath  the  pellicle,  and  the 
second  being  located  at  the  junction  of  ectoplasm  and  endoplasm. 
The  remainder  of  the  cilia  are  arranged  in  longitudinal  spiral  rows. 
The  most  anterior  cilia  of  these  rows,  i.e.,  those  nearest  the  adoral 
cilia,  are  nearly  as  sturdy  as  the  adoral  cilia  themselves.  But,  pro- 
gressing-posteriorly  in  the  rows,  the  cilia  become  continuously  smaller 
until  they  reach  their  minimum  size  at  the  base  of  the  apical  cone  of 
ectoplasm.  Likewise  the  ciliary  rootlets  become  shorter,  and  the  dis- 
tance between  the  basal  granules  and  the  secondary  enlargements  of 
the  rootlets  becomes  less  and  less  as  one  approaches  the  base  of  the 
apical  cone.  This  is  shown  in  figure  I.  The  remainder  of  the  way 
posteriorly  the  cilia  are  of  uniform  size,  and  the  secondary  enlarge- 
ment of  the  basal  apparatus  of  each  cilium  is  the  termination  of  the 
ciliary  rootlet  and  lies  in  the  granular  band  of  ectoplasm  near  its 
plane  of  junction  with  the  endoplasm. 

In  Bala/ntidium  coli  five  distinct  parts  constitute  the  complete 
neuromotor  apparatus,  namely  (1)  a  motorium  or  coordinating  cen- 
ter, embedded  in  the  ectoplasm  close  by  the  oesophagus,  and  from  it 
fibers  pass  out  to  the  oral  plug  and  the  motor  organelles ;  (2)  a  circum- 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      285 

oesophageal  fiber,  beginning  and  ending  in  the  motorium  and  giving 
off  branches  as  it  passes  through  the  oral  plug;  (3)  a  fiber  connecting 
the  adoral  cilia  and  the  cytostomal  membranelles  with  the  motorium ; 
(4)  the  adoral  ciliary  rootlets  passing  posteriorly  from  the  basal 
granules  of  the  adoral  cilia,  each  bearing  an  enlargement  where  it 
passes  from  ectoplasm  into  endoplasm,  and  finally  ending  without 
attachment  in  the  endoplasm  of  the  cell;  (5)  the  radial  fibers  taking 
origin  from  the  enlargements  of  the  adoral  ciliary  rootlets  and  passing 
radially  to  the  ectoplasmic  layer  where  they  turn  posteriorly  into  the 
granular  band. 

The  motorium  (mot.,  figs.  I  and  J)  when  viewed  in  ventral  aspect 
has  somewhat  the  appearance  of  a  reversed  letter  J.  It  lies  within 
the  ectoplasm  of  the  apical  cone,  close  to  the  ventral  and  right  walls 
of  the  oesophagus.  The  part  of  the  motorium  corresponding  to  the 
vertical  shaft  of  the  J  lies  along  the  right  wall  of  the  oesophagus,  and 
its  anterior  terminus  is  situated  just  inside  and  slightly  dorsal  from 
the  point  of  origin  of  the  right  lip  of  the  cytostome.  The  curved  end 
of  the  J  is  posterior  and  passes  ventrally  and  anteriorly  around  the 
oesophagus  and  ends  close  to  the  inner  termination  of  the  rows  of 
adoral  cilia.  In  the  middle  region  a  sharp  slit-like  constriction  is  often 
very  conspicuous.  It  is  with  the  part  of  the  motorium  anterior  to  this 
constriction,  that  the  circumoesophageal  fiber  and  the  adoral  ciliary 
fiber  have  their  origin.  The  portion  posterior  to  this  constriction  is 
quite  variable  both  in  size  and  in  stainability.  This  variation  is  very 
suggestive  of  the  behavior  of  the  parabasal  body  of  certain  flagellates 
as  described  by  Kofoid  and  McCulloch  (1916),  Swezy  (1916),  Kofoid 
and  Swezy  (1919).  These  authors  have  shown  that  the  parabasal  body 
is  not  kinetic  in  function  but  instead  is  a  reserve  or  reservoir  of 
material  easily  transformed  into  energy,  which  reservoir  fluctuates 
according  to  the  physiological  condition  of  the  animal.  No  direct 
evidence  can  here  be  advanced  establishing  such  a  function  for  this 
posterior  portion  of  the  motorium,  but  the  fact  of  its  fluctuation  in 
volume  and  its  variation  in  chemical  nature  (as  shown  by  stains) 
would  lead  one  to  suspect  that  such  an  interpretation  is  correct. 

The  oircumoesophag&al  fiber  (dr.  oes.  /.,  figs.  I  and  J)  takes  origin 
from  the  anterior  extremity  of  the  motorium  and  passes  into  the  oral 
plug.  Its  course  is  very  close  to  the  inner,  i.e.,  oesophageal,  surface 
of  the  plug.  It  encircles  the  oesophagus  completely  but  in  the  mem- 
branellar  area  it  becomes  very  hard  to  follow.  Certain  sections  (pi.  27, 
fig.  3),  however,  seem  to  show  that  it  unites  again  with  the  motorium. 
It  is  not  a  smooth  fiber  but  bears  irregular  enlargements  from  which 


286  University  of  California,  Publications  m  Zoology       [VOL.  20 

fibers  pass  both  posteriorly  and  anteriorly  into  the  ectoplasmic  mass 
of  the  oral  plug.  These  branches  make  no  observable  connections,  but 
seem  to  fade  out  in  the  ectoplasm.  Morphological  evidence  would 
indicate  that  this  portion  of  the  neuromotor  apparatus  is  concerned 
solely  with  the  activities  of  the  very  mobile  oral  plug.  The  adoral 
ciliary  fiber  (ad.  cil.  f.,  figs.  I  and  J)  also  arises  from  the  motorium. 
This  fiber  attaches  to  the  motorium  just  anterior  to  the  constriction. 
It  passes  directly  to  the  basal  granule  of  the  first  cilium  of  the  adoral 
row  from  which  it  passes  on  and  makes  connection  with  each  of  the 
basal  granules  of  the  entire  row.  It  turns  inward  following  the  row 
of  adoral  cilia  along  the  dorsal  or  left-hand  margin  of  the  membranelle 
area.  Here  its  course  is  exceedingly  hard  tq  determine,  but  like  the 
circumoesophageal  fiber,  some  sections  seem  to  show  its  connection 
with  the  posterior  end  of  the  motorium. 

The  remainder  of  the  neuromotor  system  is  not  directly  connected 
with  the  motorium.  The  adoral  ciliary  rootlets  (ad.  cil.  r.,  fig.  I)  pass 
inward  from  the  basal  granules  of  the  adoral  cilia  through  the  ecto- 
plasm of  the  apical  cone  into  the  endoplasm  and  well  into  the  posterior 
third  of  the  organism  where  they  end,  not  abruptly  but  by  fading  out. 
There  is  absolutely  no  indication  of  any  attachment  of  their  inner 
ends.  Just  posterior  to  the  middle  of  the  cell  there  is  usually  a  very 
distinct  crossing  of  the  ciliary  rootlets  from  the  opposite  sides  of  the 
peristome.  Each  of  these  adoral  ciliary  rootlets  bears  a  decided  enlarge- 
ment at  the  point  where  it  passes  from  the  ectoplasm  into  the  endoplasm. 
The  aggregation  of  these  enlargements  gives  the  appearance  in  cross- 
sections  through  this  region  (pi.  27,  fig.  6)  of  a  zone  of  large,  deeply 
staining  granules  about  the  oesophagus.  Each  of  these  enlargements 
gives  rise  to  a  fiber  which  passes  radially  outward  in  a  transverse 
plane.  These  have  been  termed  the  radial  fibers  (rad.  /.,  fig.  J ;  pi.  27, 
fig.  6).  Each  of  these  radial  fibers  as  it  passes  peripherally  connects 
with  small  enlargements  of  the  rootlets  of  the  cilia  of  the  apical  cone. 
The  rootlets  of  the  cilia  of  the  apical  cone  are  like  those  of  the  adoral 
cilia  except  that  they  shorten  progressively  as  they  near  the  periphery, 
at  which  point  they  scarcely  extend  into  the  endoplasm  at  all,  becom- 
ing identical  with  those  of  body  cilia.  Since  the  radial  fibers  and  the 
enlargements  of  the  ciliary  rootlets  lie  in  the  plane  of  contact  between 
the  ectoplasm  and  the  endoplasm  they  very  clearly  mark  the  limit  of 
the  two.  At  the  periphery  the  radial  fibers  turn  posteriorly  and 
become  lost  in  the  granular  band.  This  last  fact  is  very  suggestive, 
since  the  terminal  enlargements  of  the  rootlets  of  the  body  cilia  lie  in 
these  granular  bands. 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      287 

It  has  not  been  possible  to  demonstrate  a  posterior  continuation 
of  the  radial  fibers  within  the  granular  bands.  If  they  do  not  continue 
posteriorly,  making  connections  with  the  enlargements  of  the  rootlets 
of  the  body  cilia,  then  the  logical  alternative  seems  to  be  to  attribute 
the  function  of  conductivity  to  the  granular  band  of  ectoplasm  itself. 
There  must  be  some  means  of  conduction  of  stimuli,  for  the  body  cilia 
are  concerted  in  their  action,  though  not  to  so  high  a  degree  as  in 
the  case  of  the  cilia  of  the  apical  cone.  Protoplasm  is  generally  con- 
ceded to  have  the  power  of  conducting  stimuli.  So  here  in  Balan- 
tidium coli  there  seems  to  be  a  transition  from  conduction  by  the 
undifferentiated  protoplasm  which  serves  as  a-  matrix  for  the  ciliary 
apparatus,  to  a  condition  in  which  there  is  a  differentiation  of  the 
protoplasm  into  fibers  or  strands  to  serve  the  purpose.  Moreover,  the 
increasing  degree  of  differentiation  is  directly  correlated  with  the 
increasingly  high  degree  of  coordination  of  the  motor  organelles. 

It  will  be  seen  from  the  figures  and  the  above  description  that 
Balantidium  coli  is  equipped  with  a  notably  integrated  system  of 
fibers  bearing  such  morphological  relations  as  would  make  the  assign- 
ing to  them  of  the  function  of  coordination  perfectly  logical.  The 
motorium  is  connected  directly  only  with  the  oral  plug  and  the  adoral 
cilia.  But  through  ciliary  rootlets  and  the  radial  fibers  all  of  the 
cilia  of  the  apical  cone  are  in  connection  with  the  adoral  cilia.  And 
if  the  function  of  conductivity  may  be  attributed  to  the  granular 
bands  of  the  ectoplasm,  into  which  the  radial  fibers  turn  and  become 
lost  to  view,  and  in  which  the  enlargements  of  the  ciliary  rootlets  of 
the  body  cilia  lie,  then  all  of  the  motor  organelles  of  the  organism  are 
reached  by  the  neuromotor  apparatus,  and  by  it  the  coordination  of 
these  organelles  may  be  explained. 

Attributing  to  the  various  fibers  described  above  the  quality  of 
conductivity  and  to  the  whole  neuromotor  apparatus  the  function  of 
coordination  of  all  of  the  locomotor  organs  in  swimming  and  feeding, 
microdissection  experiments  carried  on  by  Taylor  (1920),  we  may 
consider  the  functions  of  the  various  parts  from  that  point  of  view. 
The  main  role  of  the  motorium  is  to  act  as  a  coordination  center.  The 
circumoesophageal  fiber  would  serve  to  correlate  the  movements  of  the 
oral  plug  with  those  of  the  adoral  cilia  in  feeding  and  in  avoiding- 
reactions.  The  ciliary  rootlets  and  radial  fibers  make  possible  the 
coordination  of  all  of  the  locomotor  organs  in  swimming  and  feeding, 
and  especially  the  cilia  of  the  apical  cone  which  are  employed  in  the 
boring  movement  of  the  organism. 


288  University  of  California  Publications  in  Zoology       [  VOL-  20 


DISCUSSION 

Up  to  the  present  time  systems  of  intracytoplasmic  fibers  and 
accessory  neuromotor  masses  comparable  to  that  found  in  Balantidium 
coli  have  been  fully  described  in  several  flagellates  and  a  few  ciliates. 
The  very  primitive  type  occurring  in  Naegleria  gruberi  (Schardinger) 
has  been  described  by  Wilson  (1916).  Kofoid  (1916)  and  Swezy 
(1916)  have  made  a  critical  comparative  study  of  the  motor  systems 
of  those  flagellates,  in  which  the}7  have  been  most  carefully  studied. 
That  there  is  a  striking  similarity  in  the  neuromotor  systems  of  flagel- 
lates and  ciliates  is  clearly  pointed  out  by  Yocom  (1918). 

Among  the  ciliates,  intracytoplasmic  fibers  have  been  known  for 
some  time  and  there  have  been  several  descriptions  of  them  and  several 
conflicting  views  as  to  their  function  (Engelmann,  1880;  Biitschli, 
1889;  Schuberg,  1891;  Maier,  1903;  Prowazek,  1903;  Griffin,  1910; 
Braune,  1913).  Sharp  (1914),  however,  was  the  first  to  describe  fully 
a  completely  integrated  fibrillar  system  with  a  central  neuromotor 
mass,  to  which  he  applied  the  term  neuromotor  apparatus. 

Of  the  neuromotor  apparatus  of  ciliates  that  of  Balantidium  coli 
is  the  third  to  be  quite  fully  worked  out.  In  1914  Sharp  described 
the  neuromotor  apparatus  of  Diplodinium  ecaudatum  (Fiorentini). 
This  apparatus  consists  of  six  parts.  The  central  motor  mass,  or 
motorium,  lies  in  the  area  of  thickened  ectoplasm  at  the  anterior  end 
of  the  animal  between  the  dorsal  and  adoral  membranelle  zones.  A 
fiber  connects  the  motorium  with  the  basal  granules  of  the  dorsal  mem- 
branelles,  a  branch  from  which  runs  along  the  base  of  the  inner  dorsal 
lip.  Another  fiber  connects  the  motorium  with  the  basal  granules  of 
the  adoral  membranelles.  A  set  of  opercular  fibers  leave  the  motorium 
and  pass  along  underneath  the  operculum.  Lastly,  the  motorium  has 
a  definite  connection  by  means  of  a  fiber  with  what  Sharp  called  the 
circumoesophageal  ring.  There  is  also  a  set  of  fibers  in  the  wall  of 
the  oesophagus,  which  he  termed  the  oesophageal  fibers,  and  which 
he  believed  took  their  origin  from  the  circumoesophageal  ring.  All  of 
these  structures  as  well  as  the  micronucleus  Sharp  found  had  an 
affinity  for  the  acid  fuchsin  when  Mallory's  connective  tissue  stain 
was  used. 

In  Euplotes  patella  (0.  F.  Miiller)  the  neuromotor  apparatus,  as 
described  by  Yocom  (1918),  is  made  up  of  five  distinct  parts.  The 


1922]       McDonald:  On  Balantidium  coli  and  Balantidium  suis      289 

motorium  is  a  somewhat  bilobed  mass  and  lies  in  the  ectoplasm  at 
the  anterior  end  of  the  organism  close  to  the  right  anterior  corner  of 
the  triangular  cytostome.  From  the  left  end  of  the  motorium  five 
main  longitudinal  fibers  pass  posteriorly,  diverging  slightly,  and  each 
joins  with  one  of  the  five  anal  cirri.  The  exact  relation  of  thes^  fibers 
to  the  basal  plates  of  anal  cirri  has  been  very  carefully  determined 
by  Taylor  (1920).  Leaving  the  right  end  of  the  motorium  a  fiber 
passes  to  the  membranelles  of  the  adoral  zone.  Directly  connected 
with  this  fiber  is  the  "sensory  structure"  of  the  anterior  lip.  Lastly, 
there  are  dissociated  fibers  in  connection  with  the  frontal,  ventral,  and 
marginal  cirri.  In  Euplotes,  as  in  Diplodinium,  all  parts  of  the 
neuromotor  apparatus  as  well  as  the  micronucleus  stain  brilliant  red 
with  acid  fuchsin. 

For  facilitating  comparison,  it  might  be  well  to  summarize  briefly 
the  neuromotor  apparatus  of  Balantidium  coli,  as  described  above. 
It  consists  in  this  organism  of  five  distinct  divisions.  The  motorium 
is  a  J-shaped  mass  situated  in  the  thickened  ectoplasm  of  the  anterior 
end  of  the  animal  close  to  the  cytostome  and  oesophagus.  From  it 
arises  the  circumoesophageal  fiber,  which  gives  off  branches  to  the 
oral  plug.  A  second  fiber  takes  its  origin  from  the  motorium  and 
connects  with  the  basal  granules  of  the  adoral  cilia.  The  adoral  ciliary 
rootlets  pass  inward  from  the  basal  granules  of  the  adoral  cilia,  and 
may  extend  well  into  the  posterior  third  of  the  cell.  The  radial  fibers 
take  their  origin  from  enlargements  of  the  adoral  ciliary  rootlets, 
at  the  point  where  they  enter  the  endoplasm.  They  pass  outward 
radially,  making  connection  with  the  ciliary  rootlets  of  the  cilia  of 
the  apical  cone,  and  at  the  periphery  turn  posteriorly  and  cannot 
be  traced  farther  in  the  granular  bands  of  the  ectoplasm.  As  in  the 
previous  forms  just  summarized,  the  neuromotor  apparatus  as  well  as 
the  micronucleus  of  Balantidium  coli  is  selective  for  acid  fuchsin. 

Of  the  three  examples  of  neuromotor  systems  so  far  fully  worked 
out  and  described,  each  represents  a  different  order  of  the  class 
Ciliata:  Diplodinium  being  of  the  order  Oligotricha;  Euplotes  being 
of  the  order  Hypotricha ;  and  Balantidium  being  of  the  order  Hetero- 
tricha.  Yet  in  spite  of  the  diversity  of  forms  there  is  a  remarkable 
similarity  in  the  neuromotor  system.  The  presence  of  a  motorium  is 
common  to  all  three.  In  each  of  the  three  organisms  it  is  located  at 
the  anterior  end  of  the  animal  and  lies  wholly  within  the  ectoplasm 
near  the  cytostome.  By  means  of  fibers  it  is  connected  with  a  part 
or  all  of  the  motor  organelles  of  the  animal.  Another  feature  of  the 


290  University  of  California  Publications  in  Zoology       [VOL.  20 

fibrillar  portion  of  the  apparatus  common  to  all  three  forms  is  the 
strand  connecting  the  motorium  with  all  of  the*  adoral  cilia  or  mem- 
branelles,  as  the  case  may  be.  Finally,  the  system,  in  all  cases,  shows 
an  affinity  for  acid  fuchsin. 

The  circumoesophageal  ring  present  in  Diplodinium  is  represented 
in  Balanticbium  by  the  circumoesophageal  fiber  running  through  the 
oral  plug.  The  oral  plug  forms  the  wall  of  the  greater  part  of  the 
oesophagus,  and  the  fiber  lies  very  close  to  the  oesophageal  surface. 
From  this  fiber  there  are  given  off  fibers  which  pass  both  anteriorly 
and  posteriorly  in  the  mass  of  the  oral  plug.  These  fibers  are  strik- 
ingly similar  in  location  to  the  oesophageal  fibers,  described  by  Sharp 
(1914)  in  the  wall  of  the  oesophagus  of  Diplodinium  and  believed  by 
him  to  arise  from  the  circumoesophageal  ring.  Sharp  points  out  that 
these  fibers  approach  very  close  to  the  micronucleus  though  there  was 
no  demonstrable  connection  with  it.  In  Balantidium  this  possibility 
is  precluded  by  the  shortness  of  the  oesophagus  which  in  no  case 
extends  inward  to  a  point  anywhere  near  the  micronucleus.  At  times 
when  the  organism  is  viewed  from  the  proper  angle,  the  ciliary  root- 
lets of  the  adoral  cilia  may  have  the  appearance  of  ending  in  the 
proximity  of  the  micronucleus  and  suggesting  a  connection  with  it. 
No  such  connection  exists,  however,  as  may  be  readily  demonstrated 
in  large  numbers  of  whole  mounts  and  still  better  in  sections  where 
these  rootlets  may  be  traced  far  posterior  to  the  micronucleus,  passing 
it  some  considerable  distance  away.  In  the  vegetative  phase,  it  is 
certain  that  no  structural  connection  exists  between  any  part  of  the 
neuromotor  apparatus  and  the  micronucleus. 

Of  the  three  neuromotor  systems  of  ciliates  here  considered,  that 
of  Balantidium  is  clearly  the  least  centralized,  though  none  the  less 
a  unified  structure.  In  Diplodinium  all  motor  organelles  connect 
directly  with  the  motorium,  and  in  Euplotes  the  same  is  true  of  all 
except  the  marginal  cirri  which  have  no  connection  whatever,  whereas 
in  Balantidium  only  the  adoral  cilia  have  direct  connection  with  the 
motorium  while  the  cilia  of  the  apical  cone  (and  those  of  the  body, 
too,  if  they  have  any  connection  whatever)  are  connected  with  it  only 
indirectly  through  the  radial  fibers  and  the  rootlets  of  the  adoral  cilia. 
This  lesser  degree  of  centralization  of  the  neuromotor  apparatus  may 
perhaps  be  explained  by  the  lesser  degree  of  specialization  of  locomotor 
organelles.  Whereas  in  Diplodinium  the  body  is  devoid  of  cilia  and 
the  dorsal  and  adoral  zones  of  membranelles  are  the  sole  motor  organ- 
elles, and  in  Euplotes  the  locomotor  organelles  are  restricted  to  the 
cytostomal  membranelles  and  a  few  cirri  on  the  ventral  surface,  in 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      291 

the  case  of  Balantidium  the  entire  organism,  with  the  exception  of 
the  oral  plug,  is  covered  with  cilia.  So  the  slightly  lesser  degree  of 
specialization  in  the  neuromotor  apparatus  would  be  the  logical  expec- 
tation if  modification  of  intracytoplasmic  structures  is  correlated 
with  modification  of  external  structures  with  which  they  have~a~direct 
connection  or  of  which  they  form  an  integral  part. 

From  the  point  of  view  of  efficiency,  also,  the  arrangement  in 
Balantidium  is  readily  explainable.  The  locomotor  activities  of  the 
organism  may  be  separated  into  three  main  sorts,  swimming,  feeding, 
and  boring,  this  last  very  likely  being  used  in  penetration  of  the 
intestinal  wall  of  the  host.  In  swimming  the  coordination  of  the  entire 
locomotor  apparatus  is  necessary.  In  feeding,  and  in  boring,  particu- 
larly, the  coordination  of  the  adoral  cilia  with  those  of  the  apical  cone 
is  extremely  essential.  Such  coordination  would  be  most  effectively 
brought  about  by  a  direct  connection  of  the  parts  concerned,  and  this 
direct  connection  is  accomplished  by  the  uniting  of  all  of  the  rootlets 
of  the  cilia  of  these  two  regions  by  means  of  the  radial  fibers,  without 
the  interpolation  of  the  motorium. 

Throughout  the  above  discussion  the  assumption  of  a  neural  func- 
tion for  the  neuromotor  apparatus,  i.e.,  the  power  of  conductivity  of 
stimuli  resulting  in  coordination  of  parts,  has  been  based  on  two 
general  types  of  evidence,  morphological  and  experimental.  The 
chemical  evidence,  that  is,  the  affinity  for  acid  fuchsin,  as  presented 
by  Sharp  (1914)  for  Diplodinium  and  by  Yocom  (1918)  for  Euplotes, 
seems  slightly  less  convincing  in  the  case  of  Balantidmm.  In  the  last 
named  organism  not  only  does  the  micronucleus,  which  has  no  connec- 
tion with  the  neuromotor  apparatus,  show  an  affinity  for  acid  fuchsin 
but  so  also  do  certain  cytoplasmic  inclusions,  which  if  not  food  par- 
ticles are  at  least  undoubtedly  concerned  in  some  way  with  metabolism 
and  have  no  morphological  relation  to  the  neuromotor  apparatus. 
Yocom  (1918)  states  that  there  is  more  of  the  orange  G  in  the  micro- 
nucleus  giving  it  a  different  shade  from  the  parts  of  the  neuromotor 
apparatus  in  the  case  of  Euplotes;  but  in  Balantidmm  I  have  been 
unable  to  detect  any  such  differentiation. 

Morphological  evidence  for  attributing  neural  function  to  the 
neuromotor  apparatus  has  been  clearly  presented  by  Yocom  (1918) 
in  his  discussion  of  the  apparatus  in  Euplotes.  The  evidence  found 
in  Bakmtidium  is  not  strikingly  different.  There  is  in  the  latter 
organism  the  same  intricate  relationship  between  the  neuromotor 
apparatus  and  the  motor  organelles.  The  most  active  cilia,  i.e.,  the 
adoral  cilia,  are  directly  connected  by  the  adoral  ciliary  fiber  with 


292  University  of  California  Publications  in  Zoology       [VOL.  20 

each  other  and  with  the  motorium.  The  cilia  of  the  apical  cone  are 
connected  with  the  adoral  cilia  by  the  radial  fibers  and  so  indirectly 
with  the  motorium.  In  this  case,  however,  coordination  with  the  adoral 
cilia  is  most  essential  and  this  corresponds  with  their  intimate  con- 
nection. These  morphological  interrelations  all  point  to  a  neural  func- 
tion for  the  neuromotor  apparatus. 

Very  convincing  experimental  evidence  of  the  neural  function  is 
to  be  found  in  the  results  of  Taylor's  (1920)  microdissection  experi- 
ments on  Euplotes  patella.  In  Euplotes  there  is  a  fiber  connecting  the 
adoral  membranelles  with  the  motorium,  and  also  a  fiber  connecting 
each  of  the  five  anal  cirri  with  it.  In  a  series  of  experiments  Taylor 
severed  various  ones  of  these  fibers  and  observed  very  carefully  the 
effect  on  the  movements  of  the  animal.  He  then  compared  these  move- 
ments with  the  normal  movements  which  he  had  previously  carefully 
analyzed  and  classified.  Severing  of  these  fibers  resulted  in  lack  of 
coordination  of  the  parts  thus  disconnected  and  resulted  in  abnormal 
movements.  Incision  made  in  other  parts  of  the  cell,  but  which  did 
not  sever  neuromotor  fibers  did  not  so  result.  In  the  words  of  the 
author,  "It  is  apparent,  then,  that  the  destruction  of  the  motorium 
or  the  severing  of  some  or  all  of  its  attached  fibers  is  alone  accountable 
for  modification  in  the  perfect  and  efficient  coordination  between  the 
series  of  membranelles  and  the  anal  cirri.  We  may,  therefore,  regard 
these  normal  morphological  relationships  as  conditioning  the  animal's 
usual  behavior  both  in  creeping  and  in  swimming." 

The  general  occurrence  among  Protozoa  of  protoplasmic  modifica- 
tion to  form  organelles  for  locomotion,  feeding,  digestion,  excretion, 
and  protection  has  been  known  almost  as  long  as  have  the  Protozoa 
themselves.  The  functions  of  such  organelles  have  not  been  difficult 
to  determine.  One  might  equally  well  expect  to  find  modifications 
correlated  with  the  conduction  of  stimuli,  but  the  establishing  of 
neural  function  is  not  so  easy.  This  difficulty  in  conjunction  with  the 
traditional  idea  of  the  simplicity  of  the  Protozoa  has  resulted  in  con- 
servatism in  crediting  any  intracellular  structures  with  the  function 
of  conductivity.  The  recent  detailed  morphological  studies  on  Proto- 
zoa and  the  experimental  work  of  Taylor  (1920),  however,  leave  little 
doubt  regarding  the  matter.  This  account  of  the  neuromotor  appa- 
ratus of  Balantidium  coU  and  Balantidium  suis  presents  additional 
evidence  of  the  likelihood  of  a  quite  general  occurrence,  in  the  Pro- 
tozoa, of  intracytoplasmic  specialization  resulting  in  a  more  or  less 
integrated  system  for  purposes  of  coordination. 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      293 


SUMMARY 

1.  Pigs  are  very  generally  infected  with  balantidia  as  shown  by 
the  findings  in  previous  investigations,  many  of  which  were  carried 
on  in  foreign  countries,  and  by  the  finding  of  68  per  cent  infection 
among  the  two  hundred  pigs  examined  during  the  present  investi- 
gation. 

2.  There  are  two  species  of  the  genus  Balantidium  that  are  para- 
sitic in  the  intestinal  tract  of  pigs,  namely,  Balantidium  coli  and 
Balantidium  suis  (sp.  nov.). 

3.  Balantidium  coli  is  the  species  first  described  by  Malmsten 
(1857)  from  man,  and  later  by  Leuckart  (1861)  as  a  parasite  in  pigs. 

4.  Balantidium  suis  (sp.  nov.)  has  not  hitherto  been  distinguished 
from  Balantidium  coli.     The  former  differs  from  the  latter  in  being 
more  elongate  and  being  broadest  anterior  instead  of  posterior  to  the 
equatorial  plane;  in  having  a  more  slenderly  proportioned  macro- 
nucleus  ;  and  in  having  the  mouth  displaced  ventrally,  instead  of  being 
almost  terminal,  which  causes  the  plane  of  demarcation  between  ecto- 
plasm and  endoplasm  in  this  region  to  slant  posteriorly  toward  the 
ventral  surface  instead  of  being  perpendicular  to  the  longitudinal 
axis,  as  is  the  case  in  Balantidium  coli. 

5.  So  far  as  recorded  facts  will  justify  conclusions,  it  seems  un- 
likely that  Balantidium  suis  occurs  as  a  parasite  of  man,  but  instead 
that  Balantidium  coli  is  the  cause  of  balantidiasis.  Whether  or  not  such 
is  the  case,  it  is  very  desirable  that  the  occurrence  of  the  two  species 
in  pigs  be  taken  into  account  in  future  work  on  experimental  infection, 
for  to  a  failure  to  distinguish  between  the  two  species  may  be  due 
the  seemingly  conflicting  results  of  previous  experiments. 

6.  The  cilia  of  the  two  species  are  homologous.    Variation  occurs 
in  size  and  relative  position  of  parts  only.     The  basal  apparatus  is 
essentially  diplosomic,  consisting  of  a  basal  granule  connected  by  a 
ciliary  rootlet  to  a  secondary  enlargement.    The  former  is  situated  just 
beneath  the  pellicle ;  the  latter  lies  in  the  plane  of  demarcation  between 
ectoplasm  and  endoplasm.    The  adoral  cilia  are  largest,  the  basal  granule 
and  secondary  enlargement  are  farthest  removed  from  one  another,  as 
the  ectoplasmic  thickening  is  greatest  in  this  region,  and  the  ciliary 
rootlet  may  extend  far  into  the  endoplasm.     The  cilia  of  the  apical 
cone  intergrade  between  the  adoral  cilia  and  the  body  cilia.    As  one 


294  University  of  California  Publications  in  Zoology       [VOL-  20 

progresses  posteriorly,  they  become  smaller  in  size,  the  secondary 
enlargement  approaches  the  basal  granule  as  the  ectoplasmic  layer 
becomes  thinner,  and  the  extension  of  the  rootlet  into  the  endoplasm 
becomes  shorter.  The  body  cilia  are  smallest  and  their  rootlets 
terminate  in  the  secondary  enlargement.  The  cilia  of  the  anterior 
end  are  highly  concerted  in  action.  They  beat  in  such  a  way  as  to 
give  the  animal  a  remarkable  boring  motion  which  probably  serves 
in  the  penetration  of  the  mucosa  of  the  intestine. 

7.  Both  species  possess  a  neuromotor  system.  This  is  a  highly 
developed  and  integrated  system  consisting  of  five  correlated  parts. 
The  motorium,  lying  within  the  ectoplasm  near  the  cytostome,  gives 
rise  to  a  circumoesophageal  fiber.  In  addition,  there  is  a  heavier  fiber 
which  connects  it  with  the  basal  granules  of  the  adoral  cilia.  The  root- 
lets of  the  adoral  cilia  extend  far  into  the  endoplasm,  usually  well  into 
the  posterior  one-third  of  the  cell.  Where  they  pass  from  ectoplasm 
into  endoplasm  each  adoral  ciliary  rootlet  bears  an  enlargement  and 
from  this  arises  a  radial  fiber  which  passes  to  the  periphery,  turns 
posteriorly,  and  disappears  in  the  granular  band  of  ectoplasm.  In 
passing  to  the  periphery  these  radial  fibers  connect  with  enlargements 
of  the  rootlets  of  the  cilia  of  the  apical  cone. 

Transmitted  February  26,  1921. 

Zoological  Laboratory,   University  of  California, 
Berkeley,  California. 


1922]      McDonald:  On  Balantidium  coli  and  Balantidium  suis      295 


LITERATURE  CITED 

BEL,  G.  S.,  and  COURET,  M. 

1910.  Balantidium  coli  infection  in  man.    Jour.  Infect.  Dis.,  7,  609-624,  4  pis. 
BEZZENBERGER,  E. 

1904.     Ueber  Infusorien  aus  asiatischen  Anuren.     Arch.  f.  Prot.,  3,  138-174, 

pi.  1,  23  figs,  in  text. 
BOECK,  W.  C. 

1917o.  Mitosis  in  Giardia  microti.    Univ.  Calif.  Publ.  ZooL,  18,  1-26,  pi.  1. 
1917&.  A  rapid  method  for  the  detection  of  protozoan  cysts  in  mammalian 

faeces.    Ibid.,  18,  145-149. 
BRAUNE,  E. 

1913.     Untersuchungen  iiber  die  im  Wiederkauermagen  vorkommenden  Proto- 
zoan.    Arch.  f.  Prot.,  32,  5-63,  pis.  3-6. 
BRUMPT,  E. 

1909.     Demonstration  du  role  pathogene  du  Balantidium  coli.    C.-R.  Soc.  Biol., 
Paris,  67,  103. 

BtJTSCHLI,  O. 

1889.     "Ciliata"  in  "Protozoa"  (1887-1889)  in  Bronn,  Klass.  und  Ordn.  des 

Thierreichs,  1,   (3),  1228-1841,  pis.  56-86. 
CHAGAS,  C. 

1911.  tiber  die  zyklischen  Variationen  des  Caryosomes  bei  zwei  Arten  para- 
sitischer  Cilia  ten.     Mem.  Inst.  Oswaldo  Cruz,  3,  136-144,  2  pis. 

CLAPAREDE,  E.,  and  LACHMANN,  J. 

1858.     Etudes  sur  les  infusoires  et  les  rhizopodesi.      (Geneve,  Kossmann),   1, 

247-248,  pi.  13. 
DELAGE,  Y.,  and  HEROUARD,  E. 

1896.     Traite  de  zoologie  concrete.      (Paris,  Schleichter  Freres),  1,  582,  870 

figs,  in  text.    Eef.  footnote,  404,  fig.  692. 
DOBELL,  C.  C. 

1909.  Researches  on  the  intestinal  Protozoa  of  frogs  and  toads.     Quart.  Jour. 

Micr.  Sci,  53,  201-277,  4  pis. 

DOFLEIN,    F. 

1911.     Lehrbuch  der  Protozoenkunde.      (Jena,  Fischer),  ed.  3,  xii+1043,  951 

figs,  in  text. 
EHRENBERG,  C.  G. 

1838.     Die  Infusionsthierchen  als  volkommene  Organismen.     (Leipzig,  Voss), 

xviii  +  547 ;  Atlas,  pis.  1-64. 
ENGLEMANN,  T.  W. 

1880.     Zur  Anatomic  und  Physiologic  der  Flimmerzellen.     Pfliiger's  Arch.  ges. 

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GRIFFIN,  L.  E. 

1910.  Euplotes  worcesteri  sp.   nov.,   I,   Structure.     Philippine   Jour.    Sci.,   5, 

291-312,  pis.  1-3,  13  figs,  in  text. 
JENNINGS,  H.  S. 

1908.     Heredity,  variation  and  evolution  in  Protozoa.     Proc.  Am.  Phil.  Soc., 
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JOHNSON,  H.  P. 

1893.     A  contribution  to  the  morphology  and  biology  of  the  stentors.     Jour. 

Morph.,  8,  467-562,  pis.  23-24. 
KOFOID,  C.  A.,  and  CHRISTIANSEN,  E.  B. 

1915.  On  binary  and  multiple  fission  in  Giardia  muris  (Grassi).    Univ.  Calif. 

Publ.  Zool.,  16,  30-54,  pis.  5-8,  1  fig.  in  text. 
KOFOID,  C.  A.,  and  McCuLLOCH,  I. 

1916.  On  Trypanosoma  triatomae,  a  new  flagellate  from  a  hemipteran  bug 

from  the  nests  of  the  wood  rat  Neotoma  fuscipes.    Ibid.,  16,  113-126, 
pis.  14-15. 
KOFOID,  C.  A.,  and  SWEZY,  O. 

1915.     Mitosis  and  multiple  fission  in  triehomonad  flagellates.    Proc.  Am.  Acad. 

Arts  and  Sei.,  51,  289-378,  pis.  1-8,  7  figs,  in  text. 
1919.     On   Trichonympha  campanula  nov.   sp.     Univ.   Calif.   Publ.   Zool.,   20, 

41-98,  pis.  5-12,  4  figs,  in  text. 
LEEUWENHOEK,  A.  VON. 

1708.     "Animalcula  e  stercore  ranarum."     Opera  omnia,  2,  49-64. 
LEUCKART,  E. 

1861.     Paramoecium  ooli.    Wiegemann's  Archiv,  1,  80,  pi.  5. 
LONG,  J.  A. 

1912.     Studies  on  early  stages  of  development  in  rats  and  mica     Univ.  Calif. 

Publ.  Zool.,  9,  105-136,  pis.  13-17,  11  figs,  in  text, 
MAIER,  H.  N. 

1903.     Ueber  den  feineren  Bau  der  Wimperapparate  der  Infusorien.     Arch.  f. 

Prot,  2,  73-179,  pis.  3-4. 
MALMSTEN,  P.  H. 

1857.     Infusorien  als  Intestinaltiere  beim  Menschen.     Virchow  Arch.  f.  pathol. 

Anat.,  12,  302-309,  pi.  10. 
MAUPAS,  E. 

1883.     Contribution    a    1 'etude    morphologique    et    anatonlique    des    infusoires 

cilies.    Arch.  Zool.  Exp.  et  Gen.,  (2),  1,  427-664,  pis.  19-24. 
METCALF,  M,  M. 

1908.     Opalina — anatomy  and  reproduction.     Arch.  f.  Prot.,  13,  195-375,  pis. 
14-28. 

MlNCHIN,  E.  A. 

1912.  An   introduction   to   the   study   of   the   Protozoa.      (London,    Arnold), 

xi  +  520,  194  figs,  in  text. 
NERESHEIMER,  E.  E. 

1903.     Die    Hohe    histologischer    Differenzierung    bei    heterotrichen    Ciliaten. 

Arch.  f.  Prot.,  2,  305-324,  pi.  7,  1  fig.  in  text. 
VON  PROWAZEK,  S. 

1903.     Flagellatenstudien ;     Anhang;     fibrillare     Strukturen     der     Vorticellen. 
Ibid.,  2,  195-212,  2  pis. 

1913.  Zur  Kenntnis  der   Balantidiosis.     Arch.   f.    Schiffs-u.    Tropenhyg.,   17, 

369-390,  2  pis.,  9  figs,  in  text. 
PUTTER,  A. 

1903.     Die  Flimmerbewegung.     Ergebn.  d.  Physiol.,  2,  1-102,  15  figs,  in  text. 
SAGTJCHI,  S. 

1917.  Studies  on  ciliated  cells.     Jour.  Morph.,  29,  217-268,  pis.  1-4,  1  fig.  in 

text. 


1922]      McDonald:  On  Balantidium  coU  and  Balantidium  suis      297 

SGHAUDINN,  F.,  and  JAKOBY,  M. 

1899.  Ueber   zwei   neue   Infusorien   im   Darm   des   Menschen.      Centralbl.    f. 

Bakt.,  Abt.  I,  25,  487-494,  4  figs,  in  text. 

SCHUBEEG,  A. 

1886.  Ueber  der  Bau  der  Bursaria  truncatella  mit  besonderer  Berucksichti- 
gung  der  protoplasmatischen  Structuren.  Morph.  Jahrb.,  12,  333- 
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SCHWEIER,   A. 

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SHARP,  E.  G. 

1914.  Diplodinium  ecaudatum,  with  an  account  of  its  neuromotor  apparatus. 
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1901.  Das  Balantidium  ooli  als  Erreger  chronischer  Durchfalle.     Centralbl.  f. 

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1867.  Der  Organismus  der  Infusionsthiere  nach  eigenen  Forschungen  in  sys- 
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STRONG,  E.  P. 

1904.     The  clinical  and  pathological  significance  of  Balantidium  coll.     Bureau 

Gov't.  Labs.  (Manila,  P.  I.),  Bull.  26,  77,  10  pis. 
SWEZY,  O. 

1916.     The  kinetonucleus  of  flagellates  and  the  binuclear  theory  of  Hartmann. 

Univ.  Calif.  Publ.  Zool.,  16,  185-240,  58  figs,  in  text. 
TAYLOR,  C.  V. 

1920.     Demonstration  of  the  function  of  the  neuromotor  apparatus  in  Euplotes 
by  the  method  of  microdissection.     Ibid.,  19,  403-470,  pis.  29-33,  2 
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THON,  K. 

1904.     Ueber  den  feineren  Bau  von  Didinium  nasutum  O.  F.  M.    Arch.  f.  Prot., 

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WALKER,  E.  L. 

1909.     Sporulation  in  the  parasitic  Ciliata.    Ibid.,  17,  297-306,  2  pis. 

1913.     Experimental  balantidiasis.     Philippine  Jour.  Sci.,  8,    (B),  333-349,  7 

pis. 
WILSON,  C.  W.  v 

1916.     On  the  life  history  of  a  soil  amoeba.    Univ.  Calif.  Publ.  Zool.,  16,  241- 

292,  pis.  18-23. 
WISING,  P.  J. 

1871.     Till  kannedomen  om  Balantidium  coli  hos  manniskan.     Nordiskt  Med. 

Ark.,  3,  1-30,  1  pi. 
YOCOM,  H.  B. 

1918.  The  neuromotor  apparatus  of  Euplotes  patella.  Univ.  Calif.  Publ. 
Zool.,  18,  337-396,  pis.  14-16,  1  fig.  in  text. 


EXPLANATION  OF  PLATES 

PLATE  27 

Camera  lucida  drawings  of  a  series  of  transverse  sections  of  Balantidium  coli 
(Malmsten).  The  series  begins  at  the  anterior  end  and  progresses  posteriorly 
about  one-third  the  length  of  the  organism.  X  1000. 

Fig.  1.  This  section  shows  dorsal  portion  only  of  peristome.  The  adoral  cilia 
are  removed  showing  their  basal  granules  clearly. 

Fig.  2.  A  portion  of  the  oral  plug  is  shown  with  the  circumoesophageal  fiber 
and  the  connected  oral  plug  fibers.  The  deeply-staining  region  between  proto- 
plasm of  oral  plug  and  the  surrounding  ectoplasm,  so  marked  in  this  individual, 
is  rarely  found. 

Fig.  3.  The  continuation  of  cilia  over  the  ventral  lip  and  down  into  the  cyto- 
stome  are  to  be  noted  particularly;  the  beginning  of  the  motorium  on  the 
(reader's)  left  of  the  cytostome;  and  the  connection  of  the  adoral  ciliary  fiber 
with  the  motorium. 

Fig.  4.  In  this  figure  the  cilia  of  the  cytostome  give  the  appearance  of  mem- 
branelles;  the  circumoesophageal  fiber  makes  connection  with  the  motorium. 

Fig.  5.  This  shows  the  beginnings  of  the  enlargements  of  the  adoral  ciliary 
rootlets. 

Fig.  6.  Here  the  oesophagus  is  completely  surrounded  by  the  enlargements 
and  radial  fibers  may  be  seen  arising  from  some  of  them. 

Fig.  7.  The  extreme  posterior  tip  of  the  motorium  appears  within  the  circle 
of  enlargements;  the  dorsal  half  of  this  section  is  through  the  endoplasm. 

Fig.  8.  This  section  is  posterior  to  the  adoral  apparatus  with  the  exception  of 
the  rootlets  of  the  adoral  cilia  which  in  cross-section  can  not  be  distinguished  from 
the  granules  of  the  endoplasm. 


[298J 


UNIV.    CALIF.    PUBL.     ZOOL.    VOL.    20 


[  MCDONALD  ]  PLATE  27 


PLATE  28 

Figs.  9-12.  Series  of  longitudinal  sections  through  the  anterior  end  of  Balan- 
tidium  ooli  (Malmsten).  X  1000.  These  sections  are  oblique,  being  more  nearly 
frontal  than  sagittal,  however.  The  section  shown  in  figure  9  is  tangential  to  the 
margin  of  the  peristome  some  distance  to  the  right  of  the  most  dorsal  point  of  the 
latter  (see  fig.  J  in  text).  The  remainder  progress  toward  the  left  ventral  lip. 
The  oral  plug  fibers,  the  radial  fibers,  and  the  adoral  ciliary  rootlets  are  shown 
clearly  in  these  sections. 

Fig.  13.  A  sagittal  section  through  Balantidium  suis  (sp.  nov.).  X  1000. 
The  specific  characters,  viz.,  elongate  body  and  macronucleus,  and  oblique  plane 
delimiting  apical  cone  of  ectoplasm,  are  shown  in  this  section.  The  cytopyge  is 
distinct  and  open  to  the  exterior.  A  paramylum  body  of  considerable  size  is 
present  in  the  endoplasm. 

Fig.  14.  An  oblique  longitudinal  section  through  Balantidium  coli  (Malmsten) 
showing  the  protrusion  of  the  oral  plug.  X  750. 


[300] 


UNIV.    CALIF.    PUBL.     ZOOL.    VOL.    20 


[  MCDONALD  ]   PLATE.  28 


l«f --t- ; 

^--A'^.m'':^.* 


1 1 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS—  (Continued) 

16.  The  Subclavian  Vein  and  Its  Relations  in  Elasmobranch  Fishes,  by  J.  Frank 

Daniel.    Pp.  479-484,  2  figures  in  text.    August,  1918  .  .........  ...  ..  .........  -----  ......  1" 

17   The  Cercaria  of  the  Japanese  Blood  Fluke,  Schistosoma  japomcum  Katsu- 

rada,  by  William  W.  Cort.    Pp.  485-507,  3  figures  in  text. 
18.  Notes  on  the  Eggs  and  Miracidia  of  the  Human  Schistosomes,  by  William 
W.  Cort.    Pp.  509-519,  7  figures  in  text. 

Nos.  17  and  18  in  one  cover.    January,  1919  .........................................  —      *» 

Index,  pp.  521-529. 
Vol  19.  1.  Reaction  of  Various  Plankton  Animals  with  Reference  to  Their  Diurnal 

Migrations,  by  Calvin  O.  Esterly.    Pp.  1-83.    April,  1919  ..  .......    ..........  _      .85 

2.  The  Pteropod  Desmoptcrus  pacificus  (sp.  nov.),  by  Christine  Essenberg.    Pp. 

85-88,  2  figures  in  text.    May,  1919  ................  -  .....................  •------.-•  .....  -----;-""---      *05 

3.  Studies  on  Giardia  microti,  by  William  C.  Boeck.    Pp.  85-136,  plate  1,  19 

figures  in  text.    April,  1919  .............  ....  —  .........  —  ..........................  -  .................  ----       'b° 

4  A  Comparison  of  the  Life  Cycle  of  Crimdia  with  that  of  Trypanosoma  in 

the  Invertebrate  Host,  by  Irene  McCulloch.    Pp.  135-190,  plates  2-6,  3 
figures  in  text.    October,  1919  ..........  ~  ......  -  ..........................................  V"'"-^V""^ 

5  A  Muscid  Larva  of  the  San  Francisco  Bay  Region  Which  Sucks  the  Blood 

of  Nestling  Birds,  by  O.  E.  Plath.    Pp.  191-200.    February  1919  .10 

6  Binary  Fission  in  Collodictyon  triciliatum:  Carter,  by  Robert  Clinton  Rhodes. 

Pp  201-274,  plates  7-14,  4  figures  in  text.    December,  1919  .......................  ...  91-00 

7.  The  Excretory  System  of  a  Stylet  Cercaria,  by  William  W.  Cort.    Pp.  275- 

281,  1  figure  in  text.    August,  1919  .  ..........................................  -»  .....  -"""""""""      *1U 

8.  A  New  Distome  from  Eana  aurora,  by  William  W.  Cort.     Pp.  283-298,  5 

figures  in  text.    November,  1919  ............  .  .....................................  ............  —  ---  .....     f<2° 

9   The  Occurrence  of  a  Rock-boring  Isopod  along  the  Shore  of  San  Francisco 

Bay,  California,  by  Albert  L.  Barrows.    Pp.  299-316,  plates  15-17.    De-       ^ 

10.  ACNneweMorphoioScarint"erp7etation  of  the  Structure  of  Noc'iiluca,  and  Its 
Bearing  on  the  Status  of  the  Cystofiagellata  (Haeckel),  by  Charles  A. 
Kofoid.  Pp.  317-334,  plate  18,  2  figures  in  text.  February,  1920  ...  .........  .25 

11  The  Life  Cycle  of  Echinostoma  revolutum  (Froelich),  by  John  C.  Johnson. 

Pp.  338-388,  plates  19-25,  1  figure  in  text.    May,  1920  ...........  ........ 

12  On  Some  New  Myriopods  Collected  in  India  in  1916  by  C.  A.  Kofoid,  by 

Ralph  V.  Chamberlin.    Pp.  389-402,  plates  26-28.    August,  1920  ...  .20 

13.  Demonstration  of  the  Function  of  the  Neuromotor  Apparatus  in  ^fo** 
by  the  Method  of  Microdissection,  by  Charles  V.  Taylor.    Pp.  403-470, 
plates  29-33,  2  figures  in  text.    October,  1920  ..................  .  ................................  85 

Index  In  preparation. 

Vol.20.  1.  Studies  on  the  Parasites  of  the  Termites.    I.  On  StreWomasUx  strix,  a  Poly- 
mastigote  Flagellate  with  a  Linear  Plasmodial  Phase,  by  Charles  Atwood 
Kofoid  and  Olive  Swezy.    Pp.  1-20,  plates  1-2,  1  figure  in  text.    July,  1919      .25 
2.  Studies  on  the  Parasites  of  the  Termites.    II.  On  TricJwmitus  termitidis,  a 
Polymastigote  Flagellate  with  a  Highly  Developed  Neuromotor  System, 
by  Charles  Atwood  Kofoid  and  Olive  Swezy.     Pp.  21-40,  plates  3-4,  2 
figures  in  text.    July,  1919  .................  _  .........................................  --  .......  -  ...........  --•      ? 

3  Studies  on  the  Parasites  of  the  Termites.  III.  On  TrichonympTia  campanula 
sp.  nov.,  by  Charles  Atwood  Kofoid  and  Olive  Swezy.  Pp.  41-98,  plates 
5-12,  4  figures  in  text.  July,  1919  ........  .....  ...........  ...... 

4.  Studies  on  the  Parasites  of  the  Termites.    IV.  On  Leidyopsis  sp™en™  ?en/ 

nov.   sp.  nov.,  by  Charles  Atwood  Kofoid  and  Olive  Swezy.    Pp.  99-116, 
plates  13-14,  1  figure  in  text.    July,  1919  .....  .............  • 

5.  On  the  Morphology  and  Mitosis  of  Cliilomastix  meswh  (Wenyon),  a 

Flagellate  of  the  Human  Intestine,  by  Charles  A.  Kofoid  and  Olive  Swezy. 

Pp.  117-144,  plates  15-17,  2  figures  in  text.    April,  1920  .  .......      -35 

6.  A  Critical  Review  of  the  Nomenclature  of  Human  Intestinal  Flagella  ;es, 

Cercomonas,  CMornaistix,  Trichomonas,  and  Giardia,  by  Charles  A.  Kofoid. 
Pp.  145-168,  9  figures  in  text.    June,  1920  .....  .................................  -----      • 

7.  On  the  Free,  Encysted,  and  Budding  Stages  of  Councilmania  la-fteun  a  Para- 

sitic Amoeba  of  the  Human  Intestine,  by  Charles  Atwood  Kofoid  and 
Olive  Swezy.    Pp.  169-198,  plates  18-22,  3  figures  in  text.    June,  192     —      .60 

8.  Mitosis  and  Fission  in  the  Active  and  Encysted  Phases  of  Giardia  entenca 

(Grassi)  of  Man,  with  a  Discussion  of  the  Method  of  Origin  of  Bilateral 
Symmetry  in  the  Polymastigote  FlageUates,  by  Charles  A.  Kofoid  and 
Olive  Swezy.  Pp.  199-234,  plates  23-26,  11  figures  in  text.  March, 
1922  ................................................................................................ 

9.  The  Micro-injection"of"  "Paramaecium,  by  Chas.  Wm.  Rees.     Pp.  235-242. 


10    Onaittttdm~wr^  and    Balantidium  suis    (sp.  nov.),  wth 

an   account   of   their   neuromotor    apparatus,    by    J.    Daley    McDonald. 
Pp  243-300,  plates  27,  28,  15  figures  in  text.    May,  1922  ..............................     1.00 


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11.  Mitosis  in  Endamoeba  dysenteriae  ia  the  Bone  Marrow  in  Arthritis  de- 

formans,  by  Charles  Atwood  Kofoid   and  Olive   Swezy.     Pp.   301-307, 
7  figures  in  text. 

12.  Endamoeba  dysenteriae  in  the  Lymph  Glands  of  Man  in  Hodgkin's  Disease, 

by  Charles  A.  Kofoid,  Luther  M.  Boyers,  M.D.,  and  Olive  Swezy.    Pp.  309- 
312,  4  figures  in  text. 

Nos.  11  and  12  in  one  cover.    April,  1922 .25 

VoL  21.  1.  A  Revision  of  the  Microtus  calif ornicus  Group  of  Meadow  Mice,  by  Reming- 
ton Kellogg.    Pp.  1-42,  1  figure  in  text.    December,  1918 50 

2.  Five  New  Five-Toed  Kangaroo  Rats  from  California,  by  Joseph  GrinneU. 

Pp.  43-47.    March,  1919 05 

3.  Notes  on  the  Natural  History  of  the  Bushy-tailed  Wood  Rats  of  California, 

by  Joseph  Dixon.    Pp.  49-74,  plates  1-3,  3  figures  in  text.    December,  1919      .25 

4.  Revision  of  the  Avian  Genus  Passerella,  with  Special  Reference  to  the  Dis- 

tribution and  Migration  of  the  Races  in  California,  by  H.  S.  Swarth.    Pp. 
76-224,  plates  4-7,  30  figures  in  text.    September,  1920  $1.75 

5.  A  Study  of  the  California  Jumping  Mice  of  the  Genus  Zapus,  by  A.  Brazier 

HowelL    Pp.  225-238,  1  figure  in  text.    May,  1920 _ 15 

6.  Two  New  Rodents   (Genera  Thomomys  and  Marmota)   from  the  Eastern 

Border  of  California,  by  Joseph  Grinnell.    Pp.  239-244,  6  figures  in  text, 
November,  1921 15 

7.  A  Study  of  the  Calif ornian  Forms  of  the  Microtus  montanus  Group  of 

Meadow  Mice,  by  Remington  Kellogg.     Pp.  245-274,  25  figures  in  text. 

8.  A  Synopsis  of  the  Microtus  mordax  Group  of  Meadow  Mice  in  California, 

by  Remington  Kellogg.    Pp.  275-302,  plate  8,  29  figures  in  text. 

Nos.  7  and  8  in  one  cover.    April,  1922 75 

Vol.  22.  1.  A  Quantitative  and  Statistical  Study  of  the  Plankton  of  the  San  Joaquin 

River  and  Its  Tributaries  in  and  near  Stockton,  California,  in  1913,  by 

Winfred  Emory  Allen.    Pp.  1-292,  plates  1-12,  1  figure  in  text.    June,  1920.  $3.00 
Vol.23.    The  Marine  Decapod  Crustacea  of  California,  by  Waldo  L.  Schmitt.     Pp. 

1-470,  plates  1-50,  165  figures  in  text.    May,  1921 5.00 


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